Copy-propagate, propagate-post, and propagate-prior instructions for processing vectors

ABSTRACT

The described embodiments provide a processor for generating a result vector with copied or propagated values from an input vector. During operation, the processor receives at least one input vector and a control vector. Using these vectors, the processor generates the result vector, which can contain copied propagated values from the input vector(s), depending on the value of the control vector. In addition, a predicate vector can be used to control the values that are written to the result vector.

RELATED APPLICATIONS

This application hereby claims the benefit of U.S. provisional application no. 61/089,251, entitled “Macroscalar Processor Architecture,” by inventor Jeffry E. Gonion, filed 15 Aug. 2008.

This application is related to: (1 ) pending application Ser. No. 12/419,629, entitled “Method and Apparatus for Executing Program Code,” by inventors Jeffry E. Gonion and Keith E. Diefendorff, filed on 07 Apr. 2009; (2 ) pending application Ser. No. 12/419,644, entitled “Break, Pre-Break, and Remaining Instructions for Processing Vectors,” by inventors Jeffry E. Gonion and Keith E. Diefendorff, filed on 07 Apr. 2009; (3 ) pending application Ser. No. 12/419,661, entitled “Check-Hazard Instructions for Processing Vectors,” by inventors Jeffry E. Gonion and Keith E. Diefendorff, filed on 07 Apr. 2009; (4 ) pending application Ser. No. 12/495,643, entitled “Shift-In-Right Instructions for Processing Vectors,” by inventors Jeffry E. Gonion and Keith E. Diefendorff, filed on 30 Jun. 2009; and (5 ) pending application Ser. No. 12/495,631, entitled “Increment-Propagate and Decrement-Propagate Instructions for Processing Vectors,” by inventors Jeffry E. Gonion and Keith E. Diefendorff, filed on 30 Jun. 2009.

This application is also related to: (1) pending application Ser. No. 12/237,212, entitled “Conditional Data-Dependency Resolution in Vector Processors,” by inventors Jeffry E. Gonion and Keith E. Diefendorff, filed 24 Sep. 2008; (2) pending application Ser. No. 12/237,196, entitled “Generating Stop Indicators Based on Conditional Data Dependency in Vector Processors,” by inventors Jeffry E. Gonion and Keith E. Diefendorff, filed 24 Sep. 2008; and (3) pending application Ser. No. 12/237,190, entitled “Generating Predicate Values Based on Conditional Data Dependency in Vector Processors,” by inventors Jeffry E. Gonion and Keith E. Diefendorff, filed 24 Sep. 2008.

BACKGROUND

1. Field

The described embodiments relate to techniques for improving the performance of computer systems. More specifically, the described embodiments relate to a shift-in-right instruction for processing vectors in program code.

2. Related Art

Recent advances in processor design have led to the development of a number of different processor architectures. For example, processor designers have created superscalar processors that exploit instruction-level parallelism (ILP), multi-core processors that exploit thread-level parallelism (TLP), and vector processors that exploit data-level parallelism (DLP). Each of these processor architectures has unique advantages and disadvantages which have either encouraged or hampered the widespread adoption of the architecture. For example, because ILP processors can often operate on existing program code that has undergone only minor modifications, these processors have achieved widespread adoption. However, TLP and DLP processors typically require applications to be manually re-coded to gain the benefit of the parallelism that they offer, a process that requires extensive effort. Consequently, TLP and DLP processors have not gained widespread adoption for general-purpose applications.

One significant issue affecting the adoption of DLP processors is the vectorization of loops in program code. In a typical program, a large portion of execution time is spent in loops. Unfortunately, many of these loops have characteristics that render them unvectorizable in existing DLP processors. Thus, the performance benefits gained from attempting to vectorize program code can be limited.

One significant obstacle to vectorizing loops in program code in existing systems is dependencies between iterations of the loop. For example, loop-carried data dependencies and memory-address aliasing are two such dependencies. These dependencies can be identified by a compiler during the compiler's static analysis of program code, but they cannot be completely resolved until runtime data is available. Thus, because the compiler cannot conclusively determine that runtime dependencies will not be encountered, the compiler cannot vectorize the loop. Hence, because existing systems require that the compiler determine the extent of available parallelism during compilation, relatively little code can be vectorized.

SUMMARY

The described embodiments provide a processor (e.g., processor 102 in FIG. 1) for propagating values to a result vector. During operation, the processor receives a first input vector and a control vector, and optionally receives a predicate vector. The processor then generates the result vector. When generating the result vector, if the predicate vector is received, for each element in the result vector at and to the right of a key element position for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector at and to the right of the key element position, the processor is configured so that if a corresponding element in the control vector contains a non-zero value, the processor sets the element in the result vector equal to a value in a corresponding element in the first input vector. Otherwise, if the corresponding element in the control vector contains a zero, the processor sets the element in the result vector equal to a value contained in an element at an element position in the first input vector which corresponds to the right-most relevant element to the left of the corresponding element in the control vector.

In some embodiments, if the predicate vector is received, the key element position is a leftmost element position for which both an element in the predicate vector and an element in the control vector contain non-zero values. Otherwise, the key element position is a leftmost element position for which an element in the control vector contains a non-zero value.

In some embodiments, the processor receives a second input vector. In these embodiments, if the predicate vector is received, for each element to the left of the key element for which a corresponding element in the control vector contains a zero and for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector to the left of the key element, when generating the result vector, the processor is configured to set the element in the result vector equal to a value in a corresponding element in the second input vector. In these embodiments, if no key element position exists, if the predicate vector is received, for each element in the result vector for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector, when generating the result vector, the processor is configured to set the element in the result vector equal to a value in a corresponding element in the second input vector.

In some embodiments, if the predicate vector is received, when generating the result vector, for each element in the result vector, the processor is configured to leave the element in the result vector unmodified if a corresponding element in the predicate vector contains a zero. In alternative embodiments, if the predicate vector is received, when generating the result vector, for each element in the result vector, the processor is configured to set the element in the result vector to zero if a corresponding element in the predicate vector contains a zero.

In some embodiments, when generating the result vector, the processor is configured to process elements in the input vector, control vector, and, if the predicate vector is received, the predicate vector in parallel to enable the elements of the result vector to be generated in parallel.

In some embodiments, when generating the result vector, the processor is configured to store the result vector in a processor register or a computer-readable storage medium.

In some embodiments, if the predicate vector is received, a relevant element is an element position where an element in the control vector contains a non-zero value and an element in the predicate vector contains a non-zero value. Otherwise, a relevant element is an element position where an element in the control vector contains a non-zero value.

The described embodiments provide a processor (e.g., processor 102) for propagating values to a result vector. During operation, the processor receives a first input vector, a second input vector, and a control vector, and optionally receives a predicate vector. The processor then generates the result vector. When generating the result vector, if the predicate vector is received, for each element in the result vector to the right of a key element position for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector to the right of the key element position, the processor is configured so that if a corresponding element in the control vector contains a non-zero value, the processor sets the element in the result vector equal to a value in a corresponding element in the first input vector. Otherwise, if the corresponding element in the control vector contains a zero, the processor sets the element in the result vector equal to a value contained in an element at an element position in the second input vector which corresponds to the right-most relevant element to the left of the corresponding element in the control vector.

In some embodiments, the key element position is a leftmost element position for which an element in the control vector contains a non-zero value.

In some embodiments, if the predicate vector is received, for each element for which the predicate vector contains a non-zero value at or to the left of the key element position, otherwise, for each element in the result vector at or to the left of the key element position, when generating the result vector, the processor is configured to set the element in the result vector equal to a value in a corresponding element in the first input vector. In these embodiments, if no key element position exists, if the predicate vector is received, for each element in the result vector for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector, when generating the result vector, the processor is configured to set the element in the result vector equal to a value in a corresponding element in the second input vector.

The described embodiments provide a processor (e.g., processor 102) for propagating values to a result vector. During operation, the processor receives an input vector and a control vector, and optionally receives a predicate vector. The processor then generates the result vector. When generating the result vector, if the predicate vector is received, for each element in the result vector at or to the right of a key element position for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector at or to the right of the key element position, the processor is configured so that if a corresponding element in the control vector contains a zero, the processor sets the element in the result vector equal to a value in a corresponding element in the input vector. Otherwise, if the corresponding element in the control vector contains a non-zero value, the processor sets the element in the result vector equal to a value contained in an element at an element position in the input vector which corresponds to the right-most relevant element to the left of the corresponding element in the control vector. In these embodiments, if a leftmost element in the result vector is at the key element position, for each element in the result vector to the left of a leftmost element in the result vector where a corresponding element in the control vector or the predicate vector contains a zero, the processor is configured to set the element in the result vector equal to a value in a rightmost element of the input vector.

In some embodiments, if the predicate vector is received, the key element position is a leftmost element position for which both an element in the predicate vector and an element in the control vector contain non-zero values. Otherwise, the key element position is a leftmost element position for which an element in the control vector contains a non-zero value.

In some embodiments, if the predicate vector is received, for each element in the result vector to the left of the key element for which a corresponding element in the control vector contains a zero and for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector to the left of the key element, when generating the result vector, the processor is configured to set the element in the result vector equal to a value in a corresponding element in the input vector. In these embodiments, if no key element position exists, if the predicate vector is received, for each element in the result vector for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector, when generating the result vector, the processor is configured to set the element in the result vector equal to a value in a corresponding element in the second input vector.

In some embodiments, if the predicate vector is received, a relevant element is an element position where an element in the control vector contains a zero or an element in the predicate vector contains a zero. Otherwise, a relevant element is an element position where an element in the control vector contains a zero.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 presents a block diagram of a computer system in accordance with the described embodiments.

FIG. 2 presents an expanded view of a processor in accordance with the described embodiments.

FIG. 3 presents an expanded view of a vector execution unit in accordance with the described embodiments.

FIG. 4 presents an example of the parallelization of a loop in program code in accordance with the described embodiments.

FIG. 5 presents two tables illustrating operation using vectorized code in accordance with the described embodiments.

FIG. 6 presents vectorized program code in accordance with the described embodiments.

FIGS. 7A-7B present exemplary vectorized program code in accordance with the described embodiments.

FIG. 8 presents a vectorized loop from program code with memory aliasing in accordance with the described embodiments.

FIG. 9 presents a vectorized loop from program code with memory aliasing in accordance with the described embodiments.

FIG. 10 presents a vectorized loop from program code with pseudo loop-carried dependencies in accordance with the described embodiments.

FIG. 11 presents a vectorized loop from program code with conditional updates in accordance with the described embodiments.

FIG. 12 presents a section of source code in accordance with the described embodiments.

FIGS. 13A-13B present a vectorized loop from program code with consolidation in accordance with the described embodiments.

FIG. 14 presents an example loop from program code and a dependency chart in accordance with the described embodiments.

FIG. 15 presents a vectorized loop from program code with mutual dependences in accordance with the described embodiments.

FIG. 16 presents a vectorized loop from program code with mutual dependences in accordance with the described embodiments.

FIG. 17 presents a vectorized loop from program code with summation in accordance with the described embodiments.

FIGS. 18A-18B present a vectorized loop from program code with summation in accordance with the described embodiments.

FIGS. 19A-19B present a vectorized loop from program code that has been vectorized both horizontally and vertically in accordance with the described embodiments.

FIG. 20 presents a flowchart illustrating a process for executing program code in accordance with the described embodiments.

FIG. 21 presents a flowchart illustrating a process for generating a result vector in accordance with the described embodiments.

FIG. 22 presents a flowchart illustrating a process for generating a result vector in accordance with the described embodiments.

FIG. 23 presents a flowchart illustrating a process for generating a result vector in accordance with the described embodiments.

In the figures, like reference numerals refer to the same figure elements.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the disclosed embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present embodiments. Thus, the system is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

The data structures and code herein described are typically stored on a computer-readable storage device, which may be any device or medium that can store code and/or data for use by a computer system (e.g., computer system 100). The computer-readable storage device includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing computer-readable media now known or later developed. Note that non-statutory media such as signals are not included in the computer-readable storage devices in these embodiments.

The methods and processes described in the detailed description section can be embodied as code and/or data, which can be stored in a computer-readable storage device as described above. When a computer system reads and executes the code and/or data stored on the computer-readable storage device, the computer system performs the methods and processes embodied as data structures and code and stored within the computer-readable storage medium.

Furthermore, the methods and processes described below can be included in hardware modules. For example, the hardware modules can include, but are not limited to, application-specific integrated circuit (ASIC) chips, field-programmable gate arrays (FPGAs), and other programmable-logic devices now known or later developed. When the hardware modules are activated, the hardware modules perform the methods and processes included within the hardware modules.

Terminology

Throughout the description, we use the following terminology. These terms may be generally known in the art, but are described below to clarify the subsequent descriptions.

The term “cycle” as used in this description refers to a quantum of time in which an operation happens. Although a cycle can be exactly one clock cycle, in some embodiments one “cycle” includes two or more clock cycles. Moreover, although one operation may be performed during a given cycle, that operation may include any number of sub-operations. For example, when referring to a vector execution unit performing an operation “in a cycle,” this means that sufficient time has passed to enable the execution unit to have completed the described operation.

The term “vector-length agnostic” as used in this description indicates that an operation (i.e., instruction, etc.) can be executed using vectors of any length, up to the limitations imposed by the supporting hardware. For example, assuming that the vector execution hardware supports 256-bit vectors that can include eight separate four-byte words, a vector-length agnostic operation can operate on any number of the eight words in the vector.

The term “active element,” as used in this description to refer to one or more elements of a vector, indicates elements that are operated on during a given operation. Generally, the described embodiments enable a vector execution unit to selectively perform parallel operations on one or more available elements in a given vector in parallel. For example, an operation can be performed on only the first two of eight elements of the vector in parallel. In this case, the first two elements are “active elements,” while the remaining six elements are “inactive elements.” In the described embodiments, one or more other vectors can be used to determine which elements in a given operand vector are active (i.e., are to be operated on). For example, a “predicate vector” (described in detail below) can include “active” elements that are used to determine which elements in the operand vector to perform operations on. In some embodiments, non-zero elements are active elements.

The terms “true indicator” and “false indicator” are used in this description to refer to data values (e.g., a data value contained in an element in a vector). Generally, in computer systems true and false are often represented by 1 and 0, respectively. In practice, a given embodiment could use any value to represent true and false, such as the number 55, or the letter “T.”

Computer System

FIG. 1 presents a block diagram of a computer system 100 in accordance with the described embodiments. Computer system 100 includes processor 102, L2 cache 106, memory 108, and mass-storage device 110. Processor 102 includes L1 cache 104.

Processor 102 can be a general-purpose processor that performs computational operations. For example, processor 102 can be a central processing unit (CPU) such as a microprocessor, a controller, an application-specific integrated circuit (ASIC), or a field-programmable gate array (FPGA). In the described embodiments, processor 102 has one or more mechanisms for vector processing (i.e., vector execution units). Processor 102's vector execution unit is described in detail below.

Mass-storage device 110, memory 108, L2 cache 106, and L1 cache 104 are computer-readable storage devices that collectively form a memory hierarchy that stores data and instructions for processor 102. Generally, mass-storage device 110 is a high-capacity, non-volatile memory, such as a disk drive or a large flash memory, with a large access time, while L1 cache 104, L2 cache 106, and memory 108 are smaller, faster semiconductor memories that store copies of frequently used data. Memory 108 is typically a dynamic random access memory (DRAM) structure that is larger than L1 cache 104 and L2 cache 106, whereas L1 cache 104 and L2 cache 106 are typically comprised of smaller static random access memories (SRAM). In some embodiments, L2 cache 106, memory 108, and mass-storage device 110 are shared between one or more processors in computer system 100. Such memory structures are well-known in the art and are therefore not described in more detail.

In some embodiments, the devices in the memory hierarchy (i.e., L1 cache 104, etc.) can access (i.e., read and/or write) multiple cache lines per cycle. These embodiments enable more effective processing of memory accesses that occur based on a vector of pointers or array indices to non-contiguous memory addresses.

Computer system 100 can be incorporated into many different types of electronic devices. For example, computer system 100 can be part of a desktop computer, a laptop computer, a server, a media player, an appliance, a cellular phone, a piece of testing equipment, a network appliance, a personal digital assistant (PDA), a hybrid device (i.e., a “smart phone”) or another electronic device.

Although we use specific components to describe computer system 100, in alternative embodiments different components may be present in computer system 100. For example, computer system 100 may not include some of the memory hierarchy (e.g., memory 108 and/or mass-storage device 110). Alternatively, computer system 100 may include video cards, video-capture devices, user-interface devices, network cards, optical drives, and/or other peripheral devices that are coupled to processor 102 using a bus, a network, or another suitable communication channel. Computer system 100 may also include one or more additional processors, wherein the processors share some or all of L2 cache 106, memory 108, and mass-storage device 110.

Processor

FIG. 2 presents an expanded view of processor 102 in accordance with the described embodiments. As is shown in FIG. 2, processor 102 includes L1 cache 104, integer execution unit 202, floating-point execution unit 206, and vector execution unit 204 (integer execution unit 202, floating-point execution unit 206, and vector execution unit 204 as a group are interchangeably referred to as “the execution units”). Each of the execution units is used for performing computational operations, such as logical operations, mathematical operations, or bitwise operations for an associated type of operand. More specifically, integer execution unit 202 is used for performing computational operations that involve integer operands, floating-point execution unit 206 is used for performing computational operations that involve floating-point operands, and vector execution unit 204 is used for performing computational operations that involve vector operands. Integer execution units and floating-point execution units are generally known in the art and are not described in more detail.

In the described embodiments, vector execution unit 204 is a single-instruction-multiple-data (SIMD) execution unit that performs operations in parallel on some or all of the data elements that are included in vectors of operands. FIG. 3 presents an expanded view of vector execution unit 204 in accordance with the described embodiments. As is shown in FIG. 3, vector execution unit 204 includes a vector register file 300 and an execution unit 302. Vector register file 300 includes a set of vector registers that can hold operand vectors and result vectors for execution unit 302. In some embodiments, there are 32 vector registers in the vector register file, and each register includes 128 bits. In alternative embodiments, there are different numbers of vector registers and/or different numbers of bits per register.

Execution unit 302 retrieves operands from registers in vector register file 300 and executes vector instructions that cause execution unit 302 to perform operations in parallel on some or all of the data elements in the operand vector. For example, execution unit 302 can perform logical operations, mathematical operations, or bitwise operations on the elements in the vector. Execution unit 302 can perform one vector operation per cycle (although, as described above, the “cycle” may include more than one cycle of a clock used to trigger, synchronize, and/or control execution unit 302's computational operations).

In the described embodiments, execution unit 302 supports vectors that hold N data elements (e.g., bytes, words, doublewords, etc.). In these embodiments, execution unit 302 can perform operations on N or fewer of the data elements in an operand vector in parallel. For example, assuming an embodiment where the vector is 256 bits in length, the data elements being operated on are four-byte words, and the operation is adding a value to the data elements, these embodiments can add the value to any number of the words in the vector.

In the described embodiments, execution unit 302 includes at least one control signal that enables the dynamic limitation of the data elements in an operand vector on which execution unit 302 operates. Specifically, depending on the state of the control signal, execution unit 302 may or may not operate on all the data elements in the vector. For example, assuming an embodiment where the vector is 512 bits in length and the data elements being operated on are four-byte words, the control signal can be asserted to prevent operations from being performed on some or all of 16 data words in the operand vector. Note that “dynamically” limiting the data elements in the operand vector upon which operations are performed can involve asserting the control signal separately for each cycle at runtime.

In some embodiments, based on the values contained in a vector of predicates or one or more scalar predicates, execution unit 302 applies vector operations to selected vector data elements only. In some embodiments, the remaining data elements in a result vector remain unaffected (which we call “predication”) or are forced to zero (which we call “zeroing”). In some of these embodiments, the clocks for the data element processing subsystems (“lanes”) that are unused due to predication or zeroing in execution unit 302 can be gated, thereby reducing dynamic power consumption in execution unit 302.

The described embodiments are vector-length agnostic. Thus, a compiler or programmer need not have explicit knowledge of the vector length supported by the underlying hardware (e.g., vector execution unit 302). In these embodiments, a compiler generates or a programmer writes program code that need not rely on (or use) a specific vector length (some embodiments are forbidden from even specifying a specific vector size in program code). Thus, the compiled code in these embodiments (i.e., binary code) runs on other embodiments with differing vector lengths, while potentially realizing performance gains from processors that support longer vectors. Consequently, as process technology allows longer vectors, execution of legacy binary code simply speeds up without any effort by software developers.

In some embodiments, vector lengths need not be powers of two. Specifically, vectors of 3, 7, or another number of data elements can be used in the same way as vectors with power-of-two numbers of data elements.

In the described embodiments, each data element in the vector can contain an address that is used by execution unit 302 for performing a set of memory accesses in parallel. In these embodiments, if one or more elements of the vector contain invalid memory addresses, invalid memory-read operations can occur. In these embodiments, invalid memory-read operations that would otherwise result in program termination instead cause any elements with valid addresses to be read and elements with invalid elements to be flagged, allowing program execution to continue in the face of speculative, and in hindsight illegal, read operations.

In some embodiments, processor 102 (and hence execution unit 302) is able to operate on and use vectors of pointers. In these embodiments, the number of data elements per vector is the same as the number of pointers per vector, regardless of the size of the data type. Instructions that operate on memory may have variants that indicate the size of the memory access, but elements in processor registers should be the same as the pointer size. In these embodiments, processors that support both 32-bit and 64-bit addressing modes may choose to allow twice as many elements per vector in 32-bit mode, thereby achieving greater throughput. This implies a distinct throughput advantage to 32-bit addressing, assuming the same width data path. Implementation-specific techniques can be used to relax the requirement. For example, double-precision floating-point numbers can be supported in 32-bit mode through register pairing or some other specialized mechanism.

Although we describe processor 102 as including a particular set of execution units, in alternative embodiments, processor 102 can include different numbers or types of execution units. Moreover, although the embodiment shown in FIG. 2 is limited to a particular set of functional blocks, in the described embodiments processor 102 can include other functional blocks, such as an instruction fetch unit, an instruction decode unit, a branch unit, a memory management unit, I/O interfaces, etc. coupled to the execution units. The additional functional blocks that can be present in processor 102 are well-known in the art and are not described in more detail.

Macroscalar Architecture

The described embodiments provide an instruction set and supporting hardware that allow compilers to generate program code for loops without having to completely determine parallelism at compile-time, and without discarding useful static analysis information. Specifically, these embodiments provide a set of instructions that do not mandate parallelism for loops but, instead, enable parallelism to be exploited at runtime if dynamic conditions permit. These embodiments thus include instructions that enable code generated by the compiler to dynamically switch between non-parallel (scalar) and parallel (vector) execution for loop iterations depending on conditions at runtime by switching the amount of parallelism used.

As described, these embodiments provide instructions that enable an undetermined amount of vector parallelism for loop iterations but do not require that the parallelism be used at runtime. More specifically, these embodiments include a set of vector-length agnostic instructions whose effective vector length can vary depending on runtime conditions. Thus, if runtime dependencies demand non-parallel execution of the code, then execution occurs with an effective vector length of one element. Likewise, if runtime conditions permit parallel execution, the same code executes in a vector-parallel manner to whatever degree is allowed by runtime dependencies (and the vector length of the underlying hardware). For example, if two out of eight elements of the vector can safely execute in parallel, the described embodiments execute the two elements in parallel. In these embodiments, expressing program code in a vector-length agnostic format enables a broad range of vectorization opportunities that are not present in existing systems.

In the described embodiments, during compilation, a compiler first analyzes the loop structure of a given loop in program code and performs static dependency analysis. The compiler then generates program code that retains static analysis information and instructs processor 102 how to resolve runtime dependencies and process the program code with the maximum amount of parallelism possible. More specifically, the compiler provides vector instructions for performing corresponding sets of loop iterations in parallel, and provides vector-control instructions for dynamically limiting the execution of the vector instructions to prevent data dependencies between the iterations of the loop from causing an error. This approach defers the determination of parallelism to runtime, where the information on runtime dependencies is available, thereby allowing the software and processor to adapt parallelism to dynamically changing conditions.

FIG. 4 presents an example of the parallelization of a loop in program code in accordance with the described embodiments. On the left side of FIG. 4 is shown an execution pattern for four iterations of a loop that have not been parallelized, where each loop includes instructions A-G. On the right side of FIG. 4 is shown a parallelized version of the loop in accordance with the described embodiments. In this example, we assume that each instruction within an iteration depends on at least one instruction before it, so that there is a static dependency chain between the instructions of a given iteration. Hence, the instructions within a given iteration cannot be parallelized (i.e., instructions A-G within a given iteration are always serially executed with respect to the other instructions in the iteration). Note that in alternative embodiments the instructions within a given iteration can be parallelizable.

As shown by the arrows between the iterations of the loop in FIG. 4, there is a possibility of a runtime data dependency between instruction E in a given iteration and instruction D of the subsequent iteration. However, during compilation, the compiler can only determine that the possibility of data dependency exists between these instructions. The compiler cannot tell in which iterations dependencies will actually materialize, because this information is only available at runtime. In this example, a data dependency that actually materializes at runtime is shown by the solid arrows in FIG. 4, while a data dependency that doesn't materialize at runtime is shown using a dashed arrow. Thus, as shown in FIG. 4, a runtime data dependency actually occurs between the first/second and third/fourth iterations.

Because no data dependency exists between the second and third iterations, the second and third iterations can safely be processed in parallel. Furthermore, instructions A-C and F-G of a given iteration have dependencies only within an iteration and, therefore, instruction A of a given iteration is able to execute in parallel with instruction A of any other iteration, instruction B can also execute in parallel with instruction B of any other iteration, and so forth.

The right side of FIG. 4 shows a version of the loop that has been parallelized in accordance with the observations above. The example shows how the iterations of such a loop can be executed to accommodate both the static and runtime data dependencies, while achieving maximum parallelism. For instructions A-C, all four iterations can be executed in parallel. Then instructions D and E can be executed with the maximum amount of parallelism allowed by the runtime data dependencies. Specifically, because instruction D in the second iteration depends on instruction E in the first iteration, instructions D and E in the first iteration must be executed before instruction D for the second iteration can be executed. However, because there is no data dependency between the second and third iterations, instructions D and E for these iterations can be executed in parallel. Finally, for instructions F-G, all four iterations can be executed in parallel.

Examples of the Embodiments

In the following section, we present a series of examples in describing the embodiments. These examples introduce Macroscalar operations and demonstrate their use in vectorizing loops in accordance with the described embodiments. For ease of understanding, these examples are presented using C++-formatted pseudocode.

The instructions and operations presented in this description are intended to aid in understanding the described embodiments. However, in alternative embodiments, an instruction or operation can be implemented in a different way, for example, using a microcode sequence of more primitive operations or using a different sequence of sub-operations. Note that further decomposition of instructions is avoided so that information about the macro-operation and the corresponding usage model is not obscured. Note also that additional definitions for each instruction may be provided in the “Macroscalar Instructions” section in this description.

Notation

In describing the examples, we use the following formats for variables, which are vector quantities unless otherwise noted: p5=a<b;

-   -   Elements of vector p5 are set to 0 or 1 depending on the result         of testing a<b. Note that vector p5 can be a “predicate vector,”         as described in detail below. Some instructions that generate         predicate vectors also set processor status flags to reflect the         resulting predicates. For example, the processor status flags         can include the FIRST, LAST, NONE, and/or ALL flags.         ˜p5; a=b+c;     -   Only elements in vector a designated by active (i.e., non-zero)         elements in the predicate vector p5 receive the result of b+c.         The remaining elements of a are unchanged. This operation is         called “predication,” and is denoted using the tilde (“˜”) sign         before the predicate vector.         !p5; a=b+c;     -   Only elements in vector a designated by active (i.e., non-zero)         elements in the predicate vector p5 receive the result of b+c.         The remaining elements of a are set to zero. This operation is         called “zeroing,” and is denoted using the exclamation point         (“!”) sign before the predicate vector.

if (FIRST( )) goto ...; Also LAST( ), ANY( ), ALL( ), CARRY( ), ABOVE( ), or NONE( ), (where ANY( ) == !NONE( ))

These instructions test the processor status flags and branch accordingly. x+=VECLEN;

-   -   VECLEN is a machine value that communicates the number of         elements per vector. The value is determined at runtime by the         processor executing the code, rather than being determined by         the assembler.         // Comment     -   In a similar way to many common programming languages, the         following examples use the double forward slash to indicate         comments. These comments can provide information regarding the         values contained in the indicated vector or explanation of         operations being performed in a corresponding example.

In these examples, other C++-formatted operators retain their conventional meanings, but are applied across the vector on an element-by-element basis. Where function calls are employed, they imply a single instruction that places any value returned into a destination register. For simplicity in understanding, all vectors discussed in this paper are vectors of integers, but alternative embodiments support other data formats.

Structural Loop-Carried Dependencies

Example 1 presents an example loop in program code that is “non-vectorizable” using conventional vector architectures. (Note that in addition to being non-vectorizable, this loop is also not multi-threadable on conventional multi-threading architectures due to the fine-grain nature of the data dependencies.) For clarity, this loop has been distilled to the fundamental loop-carried dependencies that make the loop unvectorizable.

In this example, the variables r and s have loop-carried dependencies that prevent vectorization using conventional architectures. Notice, however, that the loop is vectorizable as long as the condition (A[x]<FACTOR) is known to be always true or always false. These assumptions change when the condition is allowed to vary during execution (the common case). For simplicity in this example, we presume that no aliasing exists between A[ ] and B[ ]. Note that aliasing is addressed in later sections.

r = 0; s = 0; for (x=0; x<KSIZE; ++x) {   if (A[x] < FACTOR)   {     r = A[x+s];   }   else   {     s = A[x+r];   }   B[x] = r + s; }

EXAMPLE 1 Program Code Loop

In the described embodiments, the loop in Example 1 can be vectorized by partitioning the vector into segments for which the conditional (A[x]<FACTOR) does not change. Exemplary processes for partitioning such vectors, as well as exemplary instructions that enable the partitioning, are presented below. Note that for this example the described partitioning need only be applied to instructions within the conditional clause. The first read of A[x] and the final operation B[x]=r+s can always be executed in parallel across a full vector, except potentially on the final loop iteration.

We now present instructions and exemplary vectorized code in order to explain the described embodiments. The following description is generally organized so that a number of instructions are described and then one or more vectorized code samples that use the instructions are presented. In some cases, a particular type of vectorization issue is explored in a given example. dest=VectorReadInt(base, offset)

VectorReadInt is an instruction for performing a memory read operation. A vector of offsets, offset, scaled by the data size (integer in this case) is added to a scalar base address, base, to form a vector of memory addresses which are then read into a destination vector. If the instruction is predicated or zeroed, only addresses corresponding to active elements are read. In the described embodiments, reads to invalid addresses are allowed to fault, but such faults only result in program termination if the first active address is invalid. VectorWriteInt(base, offset, value)

VectorWriteInt is an instruction for performing a memory write operation. A vector of offsets, offset, scaled by the data size (integer in this case) is added to a scalar base address, base, to form a vector of memory addresses. A vector of values, value, is written to these memory addresses. If this instruction is predicated or zeroed, data is written only to active addresses. In the described embodiments, writes to illegal addresses always generate faults. dest=VectorIndex(start, increment)

VectorIndex is an instruction for generating vectors of values that monotonically adjust by the increment from a scalar starting value specified by start. This instruction can be used for initializing loop index variables when the index adjustment is constant. When predication or zeroing is applied, the first active element receives the starting value, and the increment is only applied to subsequent active elements. For example:

  x = VectorIndex(0,1);  // x = { 0 1 2 3 4 5 6 7 } dest = PropagatePostT(dest, src, pred)

The PropagatePostT instruction propagates the value of active elements in src, as determined by pred, to subsequent inactive elements of dest. Active elements, and any inactive elements that precede the first active element, remain unchanged in dest. The purpose of this instruction is to take a value that is conditionally calculated, and propagate the conditionally calculated value to subsequent loop iterations as occurs in the equivalent scalar code. For example:

  Entry: dest = { 8 9 A B C D E F } src = { 1 2 3 4 5 6 7 8 } pred = { 0 0 1 1 0 0 1 0 }   Exit: dest = { 8 9 A B 4 4 E 7 } dest = PropagatePriorF(src, pred)

The PropagatePriorF instruction propagates the value of the inactive elements of src, as determined by pred, into subsequent active elements in dest. Inactive elements are copied from src to dest. If the first element of the predicate is active, then the last element of src is propagated to that position. For example:

  Entry: src = { 1 2 3 4 5 6 7 8 } pred = { 1 0 1 1 0 0 1 0 }   Exit: dest = { 8 2 2 2 5 6 6 8 } dest = ConditionalStop(pred, deps)

The Conditional Stop instruction evaluates a vector of predicates, pred, and identifies transitions between adjacent predicate elements that imply data dependencies as specified by deps. The scalar value deps can be thought of as an array of four bits, each of which designates a possible transition between true/false elements in pred, as processed from left to right. These bits convey the presence of the indicated dependency if set, and guarantee the absence of the dependency if not set. They are:

-   -   kTF—Implies a loop-carried dependency from an iteration for         which the predicate is true, to the subsequent iteration for         which the value of the predicate is false.     -   kFF—Implies a loop-carried dependency from an iteration for         which the predicate is false, to the subsequent iteration for         which the value of the predicate is false.     -   kFT—Implies a loop-carried dependency from an iteration for         which the predicate is false, to the subsequent iteration for         which the value of the predicate is true.     -   kTT—Implies a loop-carried dependency from an iteration for         which the predicate is true, to the subsequent iteration for         which the value of the predicate is true.

The element position corresponding to the iteration that generates the data that is depended upon is stored in the destination vector at the element position corresponding to the iteration that depends on the data. If no data dependency exists, a value of 0 is stored in the destination vector at that element. The resulting dependency index vector, or DIV, contains a vector of element-position indices that represent dependencies. For the reasons described below, the first element of the vector is element number 1 (rather than 0).

As an example, consider the dependencies in the loop of Example 1. In this loop, transitions between true and false iterations of the conditional clause represent a loop-carried dependency that requires a break in parallelism. This can be handled using the following instructions:

p1 = (t < FACTOR); // p1 = { 0 0 0 0 1 1 0 0 } p2 = ConditionalStop(p1, kTF|kFT); // p2 = { 0 0 0 0 4 0 6 0 }

Because the 4th iteration generates the required data, and the 5th iteration depends on it, a 4 is stored in position 5 of the output vector p2 (interchangeably called the “dependency index vector” or “DIV”). The same applies for the 7th iteration, which depends on data from the 6th iteration. Other elements of the DIV are set to 0 to indicate the absence of dependencies. (Note that in this example the first element of the vector is element number 1.) dest=GeneratePredicates(pred, DIV)

GeneratePredicates takes the dependency index vector, DIV, and generates predicates corresponding to the next group of elements that may safely be processed in parallel, given the previous group that was processed, indicated by pred. If no elements of pred are active, predicates are generated for the first group of elements that may safely be processed in parallel. If pred indicates that the final elements of the vector have been processed, then the instruction generates a result vector of inactive predicates indicating that no elements should be processed and the ZF flag is set. The CF flag is set to indicate that the last element of the results is active. Using the values in the first example, GeneratePredicates operates as follows:

Entry Conditions: // i2 = { 0 0 0 0 4 0 6 0 } p2 = 0;  // p2 = { 0 0 0 0 0 0 0 0 } Loop2:   p2 = GeneratePredicates(p2,i2); // p2′ = { 1 1 1   1 0 0 0 0 } CF = 0, ZF = 0   if(!CARRY( )) goto Loop2// p2″ = { 0 0 0 0 1 1 0   0 } CF = 0, ZF = 0 // p2′″ = { 0 0 0 0   0 0 1 1 } CF = 1, ZF = 0

From an initialized predicate p2 of all zeros, GeneratePredicates generates new instances of p2 that partition subsequent vector calculations into three sub-vectors (i.e., p′,p″, and p′″). This enables the hardware to process the vector in groups that avoid violating the data dependencies of the loop.

FIG. 5 presents two tables illustrating operation using vectorized code in accordance with the described embodiments. The top of FIG. 5 presents a table illustrating a sequence of states through which scalar execution of the loop in Example 1 might progress using a randomized 50/50 distribution of the direction of the conditional expression. The bottom of FIG. 5 presents a table illustrating a progression of execution for Macroscalar vectorized program code in accordance with the described embodiments. In FIG. 5, the values read from A[ ] are shown using leftward-slanting hash marks, while the values written to B[ ] are shown using rightward-slanting hash marks, and values for “r” or “S” (depending on which is changed in a given iteration) are shown using a shaded background. Observe that “r” never changes while “s” is changing, and vice-versa.

Nothing prevents all values from being read from A[ ] in parallel or written to B[ ] in parallel, because neither set of values participates in the loop-carried dependency chain. However, for the calculation of r and s, elements can be processed in parallel only while the value of the conditional expression remains the same (i.e., runs of true or false). This pattern for the execution of the program code for this loop is shown in the lower portion of FIG. 5. Note that the example uses vectors eight elements in length. When processing the first vector instruction, the first iteration is performed alone (i.e., execution unit 302 processes only the first vector element), whereas iterations 1-5 are processed in parallel by execution unit 302, and then iterations 6-7 are processed in parallel by execution unit 302.

FIG. 6 presents exemplary vectorized program code in accordance with the described embodiments. In FIG. 6, the top portion contains the original source code, while the bottom portion contains vectorized code representing the operations that may be performed by the described embodiments. In the vectorized code, Loop1 is the loop from the source code, while Loop2 is the vector-partitioning loop that processes the sub-vector partitions.

In the example, array A[ ] is read and compared in full-length vectors (i.e., for a vector of N elements, N positions of array A[ ] are read at once). Vector i2 is the DIV that controls partitioning of the vector. Partitioning is determined by monitoring the predicate p1 for transitions between false and true, which indicate loop-carried dependencies that should be observed. Predicate vector p2 determines which elements are to be acted upon at any time. In this particular loop, p1 has the same value in all elements of any sub-vector partition; therefore, only the first element of the partition needs to be checked to determine which variable to update.

After variable s is updated, the PropagatePostT instruction propagates the final value in the active partition to subsequent elements in the vector. At the top of the loop, the PropagatePriorF instruction copies the last value of s from the final vector position across all elements of the vector in preparation for the next pass. Note that variable r is propagated using a different method, illustrating the efficiencies of using the PropagatePriorF instruction in certain cases.

Software Speculation

In the previous example, the vector partitions prior to the beginning of the vector-partitioning loop could be determined because the control-flow decision was independent of the loop-carried dependencies. This is not always the case. Consider the following two loops:

j = 0; for (x=0; x<KSIZE; ++x) {   if (A[x] < FACTOR)   {     j = A[x+j];   }   B[x] = j; }

EXAMPLE 2A Program Code Loop

j = 0; for (x=0; x<KSIZE; ++x) {   if (A[x+j] < FACTOR)   {     j = A[x];   }   B[x] = j; }

EXAMPLE 2B Program Code Loop

In Example 2A, the control-flow decision is independent of the loop-carried dependency chain, while in Example 2B the control flow decision is part of the loop-carried dependency chain. In some embodiments, the loop in Example 2B leads the described embodiments to speculate that the value of j will remain unchanged and compensate later if this prediction proves incorrect. In these embodiments, the speculation on the value of j does not significantly change the vectorization of the loop.

In some embodiments, the compiler can be configured to always predict no data dependencies between the iterations of the loop. In these embodiments, in the case that runtime data dependencies exist, the group of active elements processed in parallel can be reduced to represent the group of elements that may safely be processed in parallel at that time. In these embodiments, there is little penalty for mispredicting more parallelism than actually exists because no parallelism is actually lost (i.e., if necessary, the iterations can be processed one element at a time, in a non-parallel way). In these embodiments, the actual amount of parallelism is simply recognized at a later stage. dest=VectorReadIntFF(base, offset, pf)

VectorReadIntFF is a first-faulting variant of VectorReadInt. This instruction does not generate a fault if at least the first active element is a valid address. Results corresponding to invalid addresses are forced to zero, and flags pf are returned that can be used to mask predicates to later instructions that use this data. If the first active element of the address is unmapped, this instruction faults to allow a virtual memory system in computer system 100 (not shown) to populate a corresponding page, thereby ensuring that processor 102 can continue to make forward progress. dest=Remaining(pred)

The Remaining instruction evaluates a vector of predicates, pred, and calculates the remaining elements in the vector. This corresponds to the set of inactive predicates following the last active predicate. If there are no active elements in pred, a vector of all active predicates is returned. Likewise, if pred is a vector of all active predicates, a vector of inactive predicates is returned. For example:

Entry: pred = { 0 0 1 0 1 0 0 0 } Exit: dest = { 0 0 0 0 0 1 1 1 }

FIGS. 7A-7B present exemplary vectorized code in accordance with the described embodiments. The code sample shown in FIG. 7A is a vectorized version of the code in Example 2A (as presented above). The code sample shown in FIG. 7B is a vectorized version of the code in Example 2B. In the vectorized code in FIG. 7B, the read of A[ ] and subsequent comparison have been moved inside the vector-partitioning loop. Thus, these operations presume (speculate) that the value of j does not change. Only after using j is it possible to determine where j may change value. After j is updated, the remaining vector elements are re-computed as necessary to iterate through the entire vector. The use of the Remaining instruction in the speculative code sample allows the program to determine which elements remain to be processed in the vector-partitioning loop before the program can determine the sub-group of these elements that are actually safe to process (i.e., that don't have unresolved data dependencies).

The described embodiments include fault-tolerant read support. Thus, in these embodiments, processor 102 can speculatively read data from memory using addresses from invalid elements of a vector instruction (e.g, VectorReadFF) in an attempt to load values that are to be later used in calculations. However, upon discovering that an invalid read has occurred, these values are ultimately discarded and, therefore, not germane to correct program behavior. Because such reads may reference non-existent or protected memory, these embodiments are configured to continue normal execution in the presence of invalid but irrelevant data mistakenly read from memory. (Note that in embodiments that support virtual memory, this has the additional benefit of not paging until the need to do so is certain.)

In the loop shown in FIG. 7A-7B, there exists a loop-carried dependency between iterations where the condition is true, and subsequent iterations, regardless of the predicate value for the later iterations. This is reflected in the parameters of the ConditionalStop instruction.

The sample code in FIGS. 7A-7B highlights the differences between non-speculative and speculative vector partitioning. In Example 2A, memory is read and the predicate is calculated prior to the ConditionalStop. The partitioning loop begins after the ConditionalStop instruction. In Example 2B, the ConditionalStop instruction is executed inside the partitioning loop, and serves to recognize the dependencies that render earlier operations invalid. In both cases, the GeneratePredicates instruction calculates the predicates that control which elements are used for the remainder of the partitioning loop.

Memory-Based Loop-Carried Dependencies

The examples presented thus far presume the compiler was able to establish that no address aliasing existed at the time of compilation. Such determinations are often very difficult or impossible to make. The next example shows how loop-carried dependencies occurring through memory (which may include aliasing) are dealt with in the described embodiments (i.e., in the Macroscalar architecture). Consider the following loop:

for (x=0; x<KSIZE; ++x) {  r = C[x];  s = D[x];  A[x] = A[r] + A[s]; }

EXAMPLE 3 Program Code Loop

In Example 3, the compiler cannot determine at compile-time whether A[x] aliases with A[r] or A[s]. However, in the described embodiments, the compiler inserts instructions that cause the hardware to check for memory hazards at runtime and partitions the vector accordingly at runtime to ensure correct program behavior. dest=CheckHazardP(first, second, pred)

CheckHazardP examines two vectors of memory addresses (or indices) corresponding to two memory operations for potential data dependencies through memory. The vector first holds addresses for the first memory operation, and vector second holds addresses for the second operation. The predicate pred indicates which elements of second are to be operated upon. As scalar loop iterations proceed forward in time, vector elements representing sequential iterations appear left to right within vectors. CheckHazardP evaluates hazards in this context. The instruction calculates a DIV representing memory hazards between the corresponding pair of first and second memory operations. The instruction correctly evaluates write-after-read, read-after-write, and write-after-write memory hazards.

As with the ConditionalStop instruction, the element position corresponding to the iteration that generates the data that is depended upon is stored in the destination vector at the element position corresponding to the iteration that is dependent upon the data. If no data dependency exists, a zero is stored in the destination vector at the element position corresponding to the iteration that does not have the dependency. For example:

Entry: first = { 2 3 4 5 6 7 8 9 } second = { 8 7 6 5 4 3 2 1 } pred = { 1 1 1 1 1 1 1 1 } Exit: dest = { 0 0 0 0 3 2 1 0 }

Here, element 5 of the first vector (“first”) and element 3 of the second vector (“second”) both access array index 6. Therefore, a 3 is stored in position 5 of DIV. Likewise, element 6 of first and element 2 of second both access array index position 7, causing a 2 to be stored in position 6 of DIV, and so forth. A zero is stored in DIV where no data dependencies exist.

In some embodiments, the CheckHazardP instruction is configured to account for various sizes of data types. However, for clarity we describe the function of the instruction using only array index types.

The example above has three memory hazards. However, in the described embodiments, only two partitions are needed to safely process the associated memory operations. Close inspection reveals that handling the first hazard on element position 3 renders subsequent dependencies on lower or equally numbered element positions moot. For example:

Entry Conditions: // DIV = { 0 0 0 0 3 2 1 0 } // p2 = { 0 0 0 0 0 0 0 0 } p2 = GeneratePredicates(p2,DIV); // p2 = { 1 1 1 1 0 0 0 0 } p2 = GeneratePredicates(p2,DIV); // p2 = { 0 0 0 0 1 1 1 1 }

The process used by the described embodiments to analyze a DIV to determine where a vector should be broken is shown in pseudocode below. In some embodiments, processor 102 performs this calculation in parallel. For example:

List = <empty>; for (x=STARTPOS; x<VECLEN; ++x)  if (DIV[x] in List)   Break from loop;  else if (DIV[x] > 0)   Append <x> to List;

The vector may safely be processed in parallel over the interval [STARTPOS, x), where x is the position where DIV[x]>0, that is, from STARTPOS up to (but not including) position x, where STARTPOS refers to the first vector element after the set of elements previously processed. If the set of previously processed elements is empty, then STARTPOS begins at the first element.

In some embodiments, multiple DIVs may be generated in code using ConditionalStop and/or CheckHazardP instructions. The GeneratePredicates instruction, however, uses a single DIV to partition the vector. There are two methods for dealing with this situation: (1) partitioning loops can be nested; or (2) the DIV's can be combined and used in a single partitioning loop. Either approach yields correct results, but the optimal approach depends on the characteristics of the loop in question. More specifically, where multiple DIVs are expected not to have dependencies, such as when the compiler simply cannot determine aliasing on input parameters, these embodiments can combine multiple DIVs into one, thus reducing the partitioning overhead. On the other hand, in cases with an expectation of many realized memory hazards, these embodiments can nest partitioning loops, thereby extracting the maximum parallelism possible (assuming the prospect of additional parallelism exists).

In some embodiments, DIVs can be combined using a VectorMax (A, B) instruction:

i2 = CheckHazardP(a,c,p0); // i2 = { 0 0 2 0 2 4 0 0 } i3 = CheckHazardP(b,c,p0); // i3 = { 0 0 1 3 3 0 0 0 } ix = VectorMax(i2,i3); // ix = { 0 0 2 3 3 4 0 0 }

Because the elements of a DIV should only contain numbers less than the position of that element, which represent dependencies earlier in time, later dependencies only serve to further constrain the partitioning, which renders lower values redundant from the perspective of the GeneratePredicates instruction. Thus, taking the maximum of all DIVs effectively causes the GeneratePredicates instruction to return the intersection of the sets of elements that can safely be processed in parallel.

FIG. 8 presents a vectorized loop from program code with memory aliasing in accordance with the described embodiments. In this example no aliasing exists between C[ ] or D[ ] and A[ ], but operations on A[ ] may alias one another. If the compiler is unable to rule out aliasing with C[ ] or D[ ], the compiler can generate additional hazard checks. Because there is no danger of aliasing in this case, the read operations on arrays C[ ] and D[ ] have been positioned outside the vector-partitioning loop, while operations on A[ ] remain within the partitioning loop. If no aliasing actually exists within A[ ], the partitions retain full vector size, and the partitioning loop simply falls through without iterating. However, for iterations where aliasing does occur, the partitioning loop partitions the vector to respect the data dependencies, thereby ensuring correct operation.

In the example presented in FIG. 8, the hazard check is performed across the entire vector of addresses. In the general case, however, it is often necessary to check hazards between conditionally executed memory operations. The CheckHazardP instruction takes a predicate that indicates which elements of the second memory operation are active. If not all elements of the first operation are active, this CheckHazardP instruction itself can be predicated with a zeroing predicate corresponding to those elements of the first operand which are active. (Note that this yields correct results for cases where the first memory operation is predicated.)

FIG. 9 presents a vectorized loop from program code with memory aliasing in accordance with the described embodiments. As shown in FIG. 9, the top portion is a loop with a memory hazard on array E[ ]. The code conditionally reads and writes to unpredictable locations within the array. The vectorized Macroscalar code for this loop is shown in the bottom portion in accordance with the described embodiments.

In the vectorized loop, p1 and p2 are predicates indicating whether array E[ ] is to be read or written, respectively. The CheckHazardP instruction checks vectors of addresses (h and i) for memory hazards. The parameter p2 is passed to CheckHazardP as the predicate controlling the second memory operation (the write). Thus, CheckHazardP identifies the memory hazard(s) between unconditional reads and conditional writes predicated on p2. The result of CheckHazardP is zero-predicated in p1. This places zeroes in the DIV (ix) for element positions that are not to be read from E[ ]. Recall that a zero indicates no hazard. Thus, the result, stored in ix, is a DIV that represents the hazards between conditional reads predicated on p1 and conditional writes predicated on p2. This is made possible because non-hazard conditions are represented with a zero in the DIV.

Pseudo Loop-Carried Dependencies

The described embodiments can encounter pseudo loop-carried dependencies. In these embodiments, not all references to values calculated during a previous iteration are actual loop-carried dependencies. A common example is when a calculated value is compared to its value from the previous iteration. Such dependencies are merely overlapping dependencies and, hence, do not form a loop-carried dependency chain. The following loop is used as an example:

j = 0; for (x=0; x<KSIZE; ++x) {  j = A[x] + A[x+1];  if (j != last)  {   B[x] = j;  }  last = j;  if (E[x] < RANGE)   continue;  if (C[x] < FACTOR)  {   D[x] = j;  } }

EXAMPLE 4 Program Code Loop

dest=ShiftInRightP(in, vect, pred)

The ShiftInRightP instruction takes the scalar value in and places in in the leftmost position of vector vect, shifting elements of vect to the right to make room. Shifted elements are propagated across elements that have a zero-predicate in the parameter. The shifted vector is then stored to the destination register. For example:

Entry: in = 9 vect = {1 2 3 4 5 6 7 8} pred = {0 1 1 1 0 1 1 1} Exit: dest = {9 9 2 3 4 4 6 7} dest = Continue(pred)

The Continue instruction evaluates the predicate pred, and returns the logical negation of each active element. In the described embodiments, this instruction can be used to handle C-language “continue” statements. In the described embodiments, the Continue instruction performs a similar operation to the logical “not” operation. For example:

Entry: pred = {0 0 1 0 0 1 0 0} Exit: dest = {1 1 0 1 1 0 1 1}

FIG. 10 presents a vectorized loop from program code with pseudo loop-carried dependencies in accordance with the described embodiments. As shown in FIG. 10, the vector last represents a vector of last values of j. It is calculated by shifting the vector j to the right one position. The last value of j from the previous pass is kept in the scalar q and is shifted into the earliest position of last. Likewise, the ultimate value of j from the current pass is copied into the scalar q for the next pass by the “q=j” operation.

To process the “continue” statement in this loop, the predicate p1 is calculated to constrain the elements for the remainder of the loop. This is predicated on p0 so that elements previously inactive remain inactive.

Conditional Updates

The described embodiments can encounter loop-carried dependencies that occur as the result of conditionally updating variables in loops. For example, incrementing a variable in every iteration is not considered a loop-carried dependency because the variable is a priori computable by a compiler. However, if the increment occurs conditionally, then a loop-carried dependency can be created.

y = 0; for (x=0; x<KSIZE; ++x) {  B[x] = A[y];  if (A[x] < FACTOR1)   ++y;  if (y >= FACTOR2)   y = 0;  C[x] = A[y]; }

EXAMPLE 5 Program Code Loop

Note that in Example 5, the variable y is used before being updated. This is a common occurrence, but this case presents another obstacle to vectorization: a vector y must be calculated to determine the values of y before y was calculated. This loop also uses y after y is updated.

This example conditionally updates the variable y either by incrementing y or resetting y to zero. Although y is a loop-carried dependency because y is conditionally updated, it is important to note that there are two situations where its value is predictable, thereby allowing parallelism: iterations where y is incremented but not reset, and iterations where y remains unchanged. dest=IncrPropagate1(value, pred)

This instruction returns a vector corresponding to the values of a variable before the variable is incremented. Only the first active element of value is referenced in this calculation. The parameter pred designates the active elements. The post-increment value is propagated across inactive elements. For example:

Entry: value = {2 4 2 4 2 4 2 4} pred = {0 1 1 1 0 0 1 1} Exit: dest = {2 4 5 6 7 7 7 8}

As shown, the first element of the vector remains unchanged because the first value is inactive. The second element remains unchanged because the second element's value before the second element is incremented is unchanged. The first active element in value (the second element in this example) serves as the basis for calculating the remaining active elements. dest=IncrPropagate2(value, pred)

This instruction returns a vector corresponding to the value of a variable after the variable is incremented. Only the first active element of value is referenced in this calculation. The parameter pred designates which elements are active. The post-increment value is propagated across inactive elements. For example:

Entry: value = {2 4 2 4 2 4 2 4} pred = {0 1 1 1 0 0 1 1} Exit: dest = {2 5 6 7 7 7 8 9} dest = DecrPropagate1(value, pred) dest = DecrPropagate2(value, pred)

These instructions are the decrementing variants of IncrPropagate1 and IncrPropagate2, respectively. As described above, these instructions return a vector corresponding to the value of a variable before and after the variable is decremented, respectively. Only the first active element of value is referenced in this calculation. The parameter pred designates which elements are active. The post-decrement value is propagated across inactive elements.

FIG. 11 presents a vectorized loop from program code with conditional updates in accordance with the described embodiments. As shown in FIG. 11, the comparison with FACTOR1 determines whether the variable y is incremented, and the comparison with FACTOR2 determines if y is to be reset. In the vectorized code, speculative partitioning is used, speculating that variable y is not to be reset. In some embodiments, speculative partitioning always speculates in the direction that allows the most parallelism.

In the outer loop, Loop1, vector p2 is initially cleared in preparation for the GeneratePredicates instruction in Loop2. Because speculative partitioning is being used, however, any remaining elements should be determined before GeneratePredicates executes. The Remaining instruction determines the number of elements remaining to be processed. GeneratePredicates may reduce this further based on the determination of dependencies that were not available earlier.

Consolidation

It is common for variables calculated within loops to be used after the loop terminates. In the described embodiments, because the loops being vectorized are initially scalar, some vectors may need to be re-cast as scalars for subsequent use. We call this process “consolidation.” These embodiments account for the case where a loop terminates prematurely and the most recent value written to a register may not be its final value. In this case, the final scalar value of a variable may be from an earlier write that alters an element corresponding to a later iteration. For example, in Example 6 below the final scalar value for the variable r is 15. This is easily determinable because the calculations are unconditional.

for (x=0; x<10; ++x) {  r = x * 3;  if (x == 5)   break;  r = x * 2; }

EXAMPLE 6 Program Code Loop

In the following loop, calculations of r are conditional, as are the conditions that can cause premature loop termination:

x = 0; for (; x<KSIZE; ++x) {  r = 23;  for (; x<KSIZE; ++x)  {   if (A[x] < FACTOR1)    r = A[x];   if (B[x] < FACTOR2)    break;   if (C[x] < FACTOR1)    r = C[x];   if (D[x] < FACTOR2)    break;   if (E[x] < FACTOR1)    r = E[x];   if (F[x] < FACTOR2)    break;  }  if (x < KSIZE)  {   G[x] = r;  } }

EXAMPLE 7 Program Code Loop

dest=PreBreak(pred)

The PreBreak instruction evaluates the predicate pred, which indicates which iteration (if any) prematurely exits the loop via a C-style “break” instruction. The instruction returns a predicate indicating which loop iterations should be active before the break occurs. For example:

Entry: pred = { 0 0 0 1 0 1 0 0 } Exit: dest = { 1 1 1 1 0 0 0 0 } dest = Break(pred)

The Break instruction evaluates the predicatepred, which indicates which iteration (if any) prematurely exits the loop via a C-style “break” instruction. The instruction returns a predicate indicating which loop iterations should be active after the break occurs. For example:

Entry: pred = { 0 0 0 1 0 1 0 0 } Exit: dest = { 1 1 1 0 0 0 0 0 } dest = CopyPropagate(dest, src, pred)

The CopyPropagate instruction copies active elements of src, as determined by pred, into the destination dest. The copy operation effectively progresses left to right. Any inactive elements prior to the first active element remain unchanged in dest. From this point forward, active elements are copied from src to dest. For inactive elements, the last active element of src is propagated into dest. For example:

Entry: dest = { 1 2 3 4 5 6 7 8 } src = { 9 A B C D E F 0 } pred = { 0 1 1 1 0 0 1 1 } Exit: dest = { 1 A B C C C F 0 }

FIGS. 12 and 13 present a vectorized loop from program code with consolidation in accordance with the described embodiments. In these figures, FIG. 12 includes the original source code, while FIGS. 13A-13B include the vectorized code.

FIGS. 12 and 13A-13B illustrate a general case of consolidating variables in the presence of premature loop termination. For each possible early termination, both the Break and PreBreak results are recorded, predicated on any prior termination condition. Before the array G[ ] can be written, the correct value of r should be consolidated from the various conditional reads that may have occurred. To accomplish this, the shortest extent of the PreBreak conditions is used to mask the conditional read predicates, which are OR-ed together. This indicates which element of r is propagated. The CopyPropagate operation then propagates this value to the end of the vector. The scalar value of r is then extracted using the PreBreak extent that was calculated earlier.

Interdependent Read-After-Write

Data dependencies in scalar code generally occur in a simple “to-from” form. When such code is vectorized, dependencies between vector elements (corresponding to instances of scalar variables in time) remain in the to-from form. However, because executing the vector instructions can coalesce operations on variables that occur at different times in the scalar version of the code; paradoxical vector interdependencies can be created. For example, consider the example loop and the dependency chart shown in FIG. 14. In the example loop, the scalar dependencies are straightforward. The vectorization of this simple source code is complicated because in order to perform the write operation, the system needs a vector of t indices, but using the read operation to obtain a vector of t indices potentially depends on the write occurring first.

This situation is unique to vectorized code. Scalar code does not suffer this phenomenon because dependencies occur in different iterations at different times. Another situation that can cause a mutual dependency is when a write occurs before a conditional break from a loop. If the termination test depends on the write, a mutual dependency is created because the existence of the write depends on the loop not terminating prematurely.

Consider the two loops shown in Example 8A and 8B, below. Example 8A contains a write to A[ ] between two reads of A[ ]. Because the write depends on the variable k, and k is potentially dependent upon the write, a mutual dependence is created. Example 8B also has a mutual dependence, except that half of the mutual dependence is a control-flow dependency, while the other half is a data dependency. The write to B[ ] can only be allowed in iterations that should actually execute, but the break depends on the write to B[ ].

k = 99; for (x=0; x<KSIZE; ++x) {  j = A[D[x]];  A[C[x]] = j + k;  k = A[B[x]];  E[x] = k; }

EXAMPLE 8A Program Code Loop

for (x=0; x<KSIZE; ++x) {  t = A[x];  B[x] = t;  if (B[t] < FACTOR)   break;  C[x] = B[t]; }

EXAMPLE 8B Program Code Loop

dest=CheckHazardPx(first, second, pred)

CheckHazardPx evaluates two vectors of addresses/indices for potential memory hazards, where the operations may be interdependent. This instruction is similar to the CheckHazardP instruction. Unlike CheckHazardP, where each element of first is checked only against lesser-ordered elements in second, CheckHazardPx also checks equal-numbered element positions in second. If these overlap then the element position with the hazard is recorded in the next highest element position. For example:

Entry: first = { 1 2 3 4 5 6 7 8 } second = { 3 1 2 3 5 4 5 6 } pred = { 1 1 1 1 1 1 1 1 } Exit: dest = { 0 0 1 0 0 5 0 0 }

FIGS. 15-16 present two loops from program code with mutual dependences along with vectorized versions of these loops in accordance with the described embodiments. In the example shown in FIG. 15, before writing to A[C[x]] it is necessary to perform the potentially dependent read of A[B[x]] so that a vector of k can be calculated. This is accomplished with a vector-partitioning loop based on CheckHazardPx to break the vector where k actually depends on the write to A[ ]. To function correctly where a single memory location is written and then read in the same iteration, the original read is also required after the write. In practice this does not substantially affect performance because all values have been recently accessed and are in the cache. The dependence between A[D[x]] and A[B[x]] is handled with a CheckHazardP instruction. Because k is calculated in the iteration before k is used, the ShiftInRightP instruction is used to move the data into the correct element position.

In the example shown in FIG. 16, the loop may prematurely exit based on data read from B[t], which occurs after the write to B[x]. The same technique is applied as in FIG. 15, but the data read from B[t] is used to calculate whether a premature exit occurs and limit the write accordingly, thus ensuring that no writes occur for loop iterations that would not have executed in a sequential machine. Due to the possibility of premature exit, when B[t] is re-read the terminating condition should be re-calculated to ensure all loop exits are properly recognized.

Summation

A common operation is calculating the sum of a series of items. If the running sum result is referenced within the loop, the result should be calculated each step of the way. Consider the following loop where a conditional running sum is stored to array B[ ].

v = v2 = 0; for (x=0; x<KSIZE; ++x) {  if (A[x] < FACTOR1)   v = A[x];  B[v] = v2;  if (A[x] > FACTOR2 && A[x] < FACTOR3)   continue;  v2 += v; }

EXAMPLE 9 Program Code Loop

dest=RunningSum1P(base, addend, pred)

This instruction returns a vector corresponding to the value of a variable before a recursive add is performed on the variable. Only the first active element of vector base is used in this calculation. The vector parameter addend holds the values that are added to base. The vector parameter pred designates which elements are active. The post-add value is propagated across inactive elements. For example:

Entry: value = { 3 4 3 4 3 4 3 4 } addend = { 2 3 2 3 2 3 2 3 } pred = { 0 1 1 1 0 0 1 1 } Exit: dest = { 3 4 7 9 12 12 12 14 }

As shown above, the first element in the vector remains unchanged because it is inactive. The second element in the vector remains unchanged because the element retains its value before the addend is added to the element. The first active element in base (the second element in base) is the basis for the remaining calculations. dest=RunningSum2P(base, addend, pred)

This instruction returns a vector corresponding to the value of a variable after an addend gets recursively added to it. Only the first active element of base is used in this calculation. The parameter addend holds the values that are added to base. The parameter pred designates which elements are active. The post-add value is propagated across inactive elements. For example:

Entry: value = { 3 4 3 4 3 4 3 4 } addend = { 2 3 2 3 2 3 2 3 } pred = { 0 1 1 1 0 0 1 1 } Exit: dest = { 3 7 9 12 12 12 14 17 }

Along with the RunningSum operations, the described embodiments can support other operations that “run” across the vector. In these embodiments, there can be a number of instructions that encapsulate commonly used operations across the vector in a vector-length agnostic manner, thereby allowing the amount of parallelism to vary due to runtime dependencies. For example, some embodiments include a running bitwise shift instruction for those loops that perform successive shifts to process bits of a word. In these embodiments, the running-shift instruction takes the number of positions to shift as a vector parameter, as well as a predicate to indicate when shifts occur and when they do not. In addition, some embodiments include running bitwise and logical operations, such as AND/OR/XOR. Moreover, some embodiments include a running-multiply, which addresses common functions such as exponentiation, factorial, and Taylor-series expansion.

FIG. 17 presents a vectorized loop from program code with summation in accordance with the described embodiments. As shown in FIG. 17, when vectorizing the source code, the write of B[ ] is relocated to the bottom of the loop body, which allows a vector of v2 sums to be calculated before they are written. In the original loop, the value of v2 is used before the addition occurs, which first requires a RunningSum1P instruction to calculate a vector of v2 sums corresponding to the scalar values of v2 before the add occurs. After v2 is written, RunningSum2P is used to calculate a vector of v2 sums corresponding to the scalar values of v2 after the addition is performed. This second step is necessary so the next pass can use the final value, although it is often the case that it is also needed later in the same pass.

A Complex Example

Example 10, below, presents a loop in program code that includes many obstacles to conventional vectorization: pointer chasing, address aliasing, irregular memory addressing, a data-serial function, unpredictable loop exit conditions, and loop-carried dependencies. Previous examples have illustrated how the described embodiments (i.e., the Macroscalar architecture) address loop-carried dependencies, unpredictable loop termination, and irregular memory addressing. Example 10 introduces two varieties of data-serial dependency chains. The first is pointer-chasing, contained in the z=A[z] statement in the source code. While pointer-chasing itself cannot be vectorized, many loops containing pointer chasing can, as is shown in this example. The second data-serial chain is an inner loop which performs an integer square-root calculation. In this inner loop, every iteration depends on the results of the prior iteration, and the loop exit depends on the final iteration and, therefore, cannot be predicted.

y = z = 0; for (x=0; x<LIMIT; ++x)  z = A[z];  t = B[z];  tx = t;  ty = t / tx;  while (ty < tx)  {   tx = (tx + ty) / 2;   ty = t / tx;  }  if (tx < FACTOR)  {   A[y++] = tx;  } }

EXAMPLE 10 Program Code Loop

dest=VectorReadIntNF(base, offset, pf)

VectorReadIntNF is a non-faulting variant of VectorReadInt. This instruction will not generate a fault if an address is unmapped or otherwise illegal to access. Results for invalid addresses are forced to zero, and flags pf are returned that can be used to maks predicates to later instructions that use this data. If the first active element of the address is unmapped, this instruction will set the ZF flag to indicate that no data was returned.

FIGS. 18A-18B present a vectorized loop from program code with summation in accordance with the described embodiments. As shown in FIG. 18B, the instruction VectorIndex (0, 1) is used to create a DIV i2 that partitions the vector into single-element sub-vectors, serializing the pointer chase. Because the pointer chase in this case is speculative, both VectorReadIntFF and VectorReadIntNF are used to speculative chase pointers at the beginning of the loop to build a full vector of possible pointers before proceeding with the rest of the loop. Note the use of the “above” conditional branch, which loops until the end of the vector, or until the first illegal read operation.

In all previous examples, vectorization was performed “horizontally,” that is, each element of the Macroscalar vectors represents a corresponding iteration of the loop. In this example there are two loops: The outer “for” loop, and the inner “while” loop. The enclosing “for” loop is, as before, horizontally vectorized, but the inner “while” loop is vertically vectorized. In a vertically vectorized loop, the described embodiments process the iterations of the loop sequentially in time, just like a scalar loop, but the data is a vector rather than a scalar loop. In vertically vectorized loops, the vector of data being processed corresponds to multiple iterations of the enclosing loop. In other words, a horizontal vector built in the enclosing “for” loop is iterated sequentially until the termination conditions of the “while” loop are met for all elements of the vector.

Horizontal and Vertical Vectorization

In the preceding examples of the described embodiments, vertical vectorization was applied because horizontal vectorization was not possible due to serial dependence in the inner loop. However, vertical vectorization is an efficient vectorization technique in its own right, as demonstrated below.

for (x=0; x<LIMIT; ++x) {  t = A[x];  s = 0;  for (y=0; y<t; ++y)  {   s += A[x+y];  }  B[x] = s; }

EXAMPLE 11 Program Code Loop

The loop in Example 11 encloses a simple summation loop, which is both horizontally and vertically vectorized to illustrate the operations performed by the described embodiments. When the inner loop is horizontally vectorized, a scalar region is crafted around the inner loop that removes it from the surrounding vector context.

FIGS. 19A-19B present a vectorized loop from program code that has been vectorized both horizontally and vertically in accordance with the described embodiments. Note that the code from Example 11 above is the code that has been vectorized in the examples in FIGS. 19A-19B.

Classifying Loops

Some embodiments classify loops according to the dependencies that affect the vectorization of the loop. For example, in some embodiments, many loops, vectorizable or not, fall into one or more of these classifications:

-   -   Classically vectorizable loops: These loops contain no         loop-carried dependencies (LCD's) other than induction         variables.     -   Loops containing associative loop-carried dependencies (LCDs):         These loops contain LCDs over an associative operation. The LCD         may be executed conditionally or unconditionally. However, if         the LCD is conditionally executed, the condition must not form         part of the LCD chain. For example, these LCDs can be reduction         operations.     -   Loops containing conditional LCDs: These loops contain LCDs that         are executed conditionally, which may take the form of multiple         conditionally-interacting LCDs or conditionally executed         non-associative LCDs. In some embodiments, these LCDs represent         control-flow hazards.     -   Loops containing memory hazards (potential LCDs): These loops         may contain actual address aliasing or addressing that the         compiler could not adequately disambiguate aliasing for         (may-alias).     -   Loops for which the degree of parallelism depends on LCD values:         These are loops for which the values of the LCDs result in other         run-time dependencies which affect the amount of available         parallelism in the loop. These loops are typically vectorized         using the above-described software speculation techniques.     -   Loops containing non-associative LCDs: This category includes         LCDs such as Newton-Raphson convergence and pointer-chasing.         These dependencies are generally vectorized using vertical         vectorization. Where vertical vectorization is not possible, the         loop may be partially vectorizable by serializing the         loop-carried dependency and vectorizing the remainder of the         loop.         Vectorizing Functions and Function Calls

In some embodiments, the compiler can replicate a function with a conventional scalar interface (i.e., a version of the function with scalar inputs and outputs) and create a secondary version with a vector interface (or can create a version with the vector interface alone). Such functions are typically vertically vectorized, for efficiency and simplicity, although horizontal vectorization may also be applied. In these embodiments, function vectorization is most easily achieved in cases where the function has no side effects on global, file-scope static, or function-local static storage. Functions using straight-line code (without loops) can also be vertically vectorized, operating on either full or partial vectors under the control of a predicate passed to the function in the compiler-generated vector interface.

If only “safe” functions are vectorized, the existence of the secondary variant guarantees that the function can safely and effectively be called from within a vectorized loop. Thus, in the described embodiments, Macroscalar vectorization techniques can be applied to vectorize commonly used functions such as sin( ), cos( ), tan( ), atan( ), sqrt( ), etc. Doing so enables loops using these functions to call vector variants with vector interfaces, rather than incurring the bottleneck of a scalar interface.

While the scheme above works for file-local functions, library functions like sin( ) have interfaces established through header files. Because compilers in the described embodiments generally do not make autonomous modification of header files, in some embodiments, an annotation mechanism, such as compiler-generated XML files stored in standardized locations, provides additional compiler-generated source-level input describing the secondary compiler-generated vector function interfaces. In these embodiments, the compiler attempts to open these annotation files implicitly upon inclusion of the appropriate header file. For example, upon inclusion of the header file <stdlib.h>, the compiler also attempts to load <stdlib.xml>. If the file did not exist, then the compiler presumes that no vector interfaces existed.

In the described embodiments, the annotation mechanism also has the potential to enable vectorization in other ways. For example, assume a loop calling two functions, one at the top of the loop body, foo( ), and the other near the bottom, bar( ). In the absence of any deep information about these functions beyond their interfaces, the compiler is forced to generate program code wherein the functions and the entire body of code between them execute serially, one element at a time. For example, foo( ) might call srand( ), while bar( ) might call rand( ). Calling srand( ) multiple times before calling rand( ) is incorrect. If, on the other hand, the functions modify no non-local state, the compiler vectorizes the code between the two function calls. The annotation scheme mentioned above can be extended to provide information about the functions and their descendants that enable the compiler to vectorize such code.

In the extended annotation scheme in the described embodiments, attributes of functions are propagated up through their callers to communicate key information to the compiler about all the functions called from a loop. Information as to whether the functions modify function-scope static variables, pointed-to function parameters, file-scope static variables, or global variables is enormously valuable. For file-scope static variables, for example, the type of reference (read or write), the name of the variable, and the file where they are located might be communicated. For global variables, only the name and type of reference is necessary. Knowledge that a function modifies no parameters or static state enables the compiler in the described embodiments to forgo enforcement of atomicity on that function, thereby removing that obstacle to vectorization.

The process in these embodiments is caller-guaranteed-correctness, assisted by trustable hints about the functions being called. The absence of a hint may cause the preclusion of an optimization, but is always safe. In these embodiments, annotations begin at the bottom level of the library, because non-annotated functions propagate uncertainty upward, disabling many opportunities for vectorization.

Instruction Definitions

The following section contains exemplary instructions used in the described embodiments (i.e., that are included in Macroscalar architecture). The described instructions demonstrate the concepts used in implementing the Macroscalar architecture and therefore do not comprise a complete list of the possible instructions. A person of skill in the art will recognize that these concepts may be implemented using different arrangements or types of instructions without departing from the spirit of the described embodiments.

Unlike conventional single-instruction-multiple-data (SIMD) coding, in some embodiments, Macroscalar code can combine vector variables with scalar registers or immediate values. Thus, in these embodiments, Macroscalar instructions can directly reference scalar registers and immediate values without making unnecessary vector copies of them. Note that this can help avoid unnecessary vector-register pressure within a loop because more vector registers can be available instead of being required for making vector copies of scalars or immediate values.

We describe these instructions using a signed-integer data type. However, in alternative embodiments, other data types or formats are used. Moreover, although Macroscalar instructions may take vector, scalar, or immediate arguments in practice, only vector arguments are shown here to avoid redundancy.

The descriptions of the instructions reference vector elements with a zero-based numbering system (i.e., element “0” is the first element). However, certain instructions, such as those involved in the processing of DIVs, express dependencies using 1-based element numbering, even though they are actually implemented using 0-based element numbering. Care should be taken to avoid confusing the language the results are expressed in from the language used to implement the instructions.

For the purposes of explanation, the vector data type is defined as a C++ class containing an array v[ ] of elements that comprise the vector. Within these descriptions, the variable VECLEN indicates the size of the vector. In some embodiments, VECLEN is constant.

In the following examples, predication is communicated to the instructions via two variables. The vector gpred is the predicate vector that affects the instruction and/or the assignment of the result vector. A scalar variable, gPredFlag, indicates whether gpred functions in a predication or zeroing capacity. This variable is set to 0 when a zeroing predicate is being applied, or is set to 1 otherwise. Additionally, some instructions may reference gpred to affect the operation of the instruction apart from the final assignment. If an instruction is not predicated, then all elements are considered active, and the vector gpred contains all true indicators.

Note that the format of the following instruction definitions is a statement of the instruction type followed by a description of the instruction that can include example code as well as one or more usage examples.

Vector Assignment

During vector assignment, active vector elements, as determined by optional predication, are copied into a destination vector. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication.

Predication and zeroing are applied at the assignment of the result vector. Final assignment of the result vector is an implicit or explicit part of every instruction that produces a result. Note that the assignment operator performs this function where predication or zeroing is not performed explicitly by the instruction.

const Vector Vector::operator = (const Vector &val) {  for (int x=0; x<VECLEN; ++x)   if (gPred.v[x])    v[x] = val.v[x];   else    v[x] &= −gPredFlag; // Not changed if    predicated, 0 if zeroed  return(*this); }

EXAMPLES

 ~p0; a = b;  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 1 2 3 4 5 6 7 8 }  On Exit: a = { 9 9 3 4 5 6 9 9 }  !p0; a = b;  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 1 2 3 4 5 6 7 8 }  On Exit: a = { 0 0 3 4 5 6 0 0 } Scalar Assignment

A scalar register or immediate value is copied into active elements of the destination vector, as determined by optional predication. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication.

const Vector & Vector::operator = (const _nt val) {  int x;  for (x=0; x<VECLEN; ++x)   if (gPred.v[x])    v[x] = val;   else    v[x] &= −gPredFlag; // Not changed if    predicated, 0 if zeroed  return(*this); }

EXAMPLES

 ~p0; a = b;  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = 5  On Exit: a = { 9 9 5 5 5 5 9 9 }  !p0; a = b;  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = 5  On Exit: a = { 0 0 5 5 5 5 0 0 } Scalar-Vector Assignment (Vector cast to Scalar)

This instruction casts a vector of values into a scalar register. Only the last active element, as determined by optional predication, is copied to the scalar destination. If no elements are active, this instruction returns the first element of the vector.

Vector::operator int (void) const {  int x,rc;   for (x=VECLEN−1; x>=0; −−x) // Locate last   active element    if (gPred.v[x])     break;    rc = v[0]; // Use first element if there    are no active ones    if (x >= 0)     rc = v[x];  return(rc); }

EXAMPLES

 ~p0; a = int(b);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = 2 b = { 1 2 3 4 5 6 7 8 }  On Exit: a = 6  !p0; a = int(b);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = 2 b = { 1 2 3 4 5 6 7 8 }  On Exit: a = 6 VectorNeg

This instruction mathematically negates active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector VectorNeg(const Vector &ob) {   Vector result;   for (int x=0; x<VECLEN; ++x)     result.v[x] = −ob.v[x];   return(result); }

EXAMPLES

 ~p0; a = −b;  On Entry: p0 = {  0  0  1 1  1  1 0 0 } a = {  9  9  9 9  9  9 9 9 } b = { −3 −2 −1 0  1  2 3 4 }  On Exit: a = {  9  9  1 0 −1 −2 9 9 }  !p0; a = −b;  On Entry: p0 = {  0  0  1 1  1  1 0 0 } a = {  9  9  9 9  9  9 9 9 } b = { −3 −2 −1 0  1  2 3 4 }  On Exit: a = {  0  0  1 0 −1 −2 0 0 } VectorNot

This instruction logically negates active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector VectorNot(const Vector &ob) {   Vector result;   for (int x=0; x<VECLEN; ++x)     result.v[x] = !ob.v[x];   return(result); }

EXAMPLES

 ~p0; a = VectorNot (b);  On Entry: p0 = { 0  0  1 1 1 1 0 0 } a = { 9  9  9 9 9 9 9 9 } b = { 0 −2 −1 0 1 2 3 0 }  On Exit: a = { 9  9  0 1 0 0 9 9 }  !p0; a = VectorNot (b);  On Entry: p0 = { 0  0  1 1 1 1 0 0 } a = { 9  9  9 9 9 9 9 9 } b = { 0 −2 −1 0 1 2 3 0 }  On Exit: a = { 0  0  0 1 0 0 0 0 } VectorInv

This instruction performs bitwise inversion active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector VectorInv(const Vector &ob) {   Vector result;   for (int x=0; x<VECLEN; ++x)     result.v[x] = ~ob.v[x];   return(result); }

EXAMPLES

 ~p0; a = ~b;  On Entry: p0 = {  0  0  1  1  1  1 0 0 } a = {  9  9  9  9  9  9 9 9 } b = { −3 −2 −1  0  1  2 3 4 }  On Exit: a = {  9  9  0 −1 −2 −3 9 9 }  !p0; a = ~b; On Entry: p0 = {  0  0  1  1  1  1 0 0 } a = {  9  9  9  9  9  9 9 9 } b = { −3 −2 −1  0  1  2 3 4 }  On Exit: a = {  0  0  1  0 −1 −2 0 0 } VectorAdd

This instruction performs addition on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. In this implementation, the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorAdd (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] + val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if zeroed   return(*result); }

EXAMPLES

 ~p0; a = b + c;  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }  On Exit: a = { 9 9 8 8 8 8 9 9 }  !p0; a = b + c;  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 } On Exit: a = { 0 0 8 8 8 8 0 0 } VectorSub

This instruction performs subtraction on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorSub (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] − val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if zeroed   return(*result); }

EXAMPLES

 ~p0; a = b − c;  On Entry: p0 = { 0 0 1 1 1  1 0 0 } a = { 9 9 9 9 9  9 9 9 } b = { 8 7 6 5 4  3 2 1 } c = { 0 1 2 3 4  5 6 7 }  On Exit: a = { 9 9 4 2 0 −2 9 9 }  !p0; a = b − c;  On Entry: p0 = { 0 0 1 1 1  1 0 0 } a = { 9 9 9 9 9  9 9 9 } b = { 8 7 6 5 4  3 2 1 } c = { 0 1 2 3 4  5 6 7 }  On Exit: a = { 0 0 4 2 0 −2 0 0 } VectorMult

This instruction performs multiplication on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorMult (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] * val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if zeroed   return(*result); }

EXAMPLES

~p0; a = b * c;  On Entry: p0 = { 0 0  1  1  1  1 0 0 } a = { 9 9  9  9  9  9 9 9 } b = { 8 7  6  5  4  3 2 1 } c = { 0 1  2  3  4  5 6 7 }  On Exit: a = { 9 9 12 15 16 15 9 9 }  !p0; a = b * c;  On Entry: p0 = { 0 0  1  1  1  1 0 0 } a = { 9 9  9  9  9  9 9 9 } b = { 8 7  6  5  4  3 2 1 } c = { 0 1  2  3  4  5 6 7 }  On Exit: a = { 0 0 12 15 16 15 0 0 } VectorDiv

This instruction performs division on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorDiv (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] / val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if Zeroed   return(*result); }

EXAMPLES

~p0; a = b / c;  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }  On Exit: a = { 9 9 3 1 1 0 9 9 }  !p0; a = b / c;  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }  On Exit: a = { 0 0 3 1 1 0 0 0 } VectorMod

This instruction performs a modulus operation on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorMod (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] % val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if Zeroed   return(*result); }

EXAMPLES

  ~p0; a = b % c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 9 9 0 2 0 3 9 9 }   !p0; a = b % c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 0 0 0 2 0 3 0 0 } VectorAnd

This instruction performs a bitwise “and” on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorAnd (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] & val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if zeroed   return(*result); }

EXAMPLES

  ~p0; a = b & c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 9 9 2 1 4 1 9 9 }   !p0; a = b & c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 0 0 2 1 4 1 0 0 } VectorOr

This instruction performs a bitwise “or” on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorOr (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] | val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if zeroed   return(*result); }

EXAMPLES

  ~p0; a = b | c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 9 9 6 7 4 7 9 9 }  !p0; a = b | c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 0 0 6 7 4 7 0 0 } VectorXor

This instruction performs a bitwise “xor” on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorXor (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] {circumflex over ( )} val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if zeroed   return(*result); }

EXAMPLES

  ~p0; a = b {circumflex over ( )} c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 9 9 4 6 0 6 9 9 }   !p0; a = b {circumflex over ( )} c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 0 0 4 6 0 6 0 0 } VectorShL

This instruction performs a bitwise left-shift on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorShL (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] << val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if zeroed   return(*result); }

EXAMPLES

  ~p0; a = b << c;   On Entry: p0 = { 0 0  1  1  1  1 0 0 } a = { 9 9  9  9  9  9 9 9 } b = { 8 7  6  5  4  3 2 1 } c = { 0 1  2  3  4  5 6 7 }   On Exit: a = { 9 9 24 40 64 96 9 9 }   !p0; a = b << c;   On Entry: p0 = { 0 0  1  1  1  1 0 0 } a = { 9 9  9  9  9  9 9 9 } b = { 8 7  6  5  4  3 2 1 } c = { 0 1  2  3  4  5 6 7 }   On Exit: a = { 0 0 24 40 64 96 0 0 } VectorShR

This instruction performs a bitwise right-shift on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Vector VectorShR (const Vector &ob, const Vector &val, Vector *result) {   for (int x=0; x<VECLEN; ++x)     if (gPred.v[x])       result->v[x] = (ob.v[x] >> val.v[x]);     else       result->v[x] &= −gPredFlag; // Not       changed if predicated, 0 if zeroed   return(*result); }

EXAMPLES

  ~p0; a = b {circumflex over ( )} c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 9 9 1 0 0 0 9 9 }   !p0; a = b {circumflex over ( )} c;   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 0 0 1 0 0 0 0 0 } VectorMin

This instruction performs a “min” operation on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector VectorMin(Vector &a, Vector &b) {   Vector r;   for (int x=0; x<VECLEN; ++x)     if (a.v[x] < b.v[x])       r.v[x] = a.v[x];     else       r.v[x] = b.v[x];   return(r); }

EXAMPLES

  ~p0; a = VectorMin(b,c);   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 9 9 2 3 4 3 9 9 }   !p0; a = VectorMin(b,c);   On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 8 7 6 5 4 3 2 1 } c = { 0 1 2 3 4 5 6 7 }   On Exit: a = { 0 0 2 3 4 3 0 0 } VectorMax

This instruction performs a “max” operation on active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector VectorMax(Vector &a, Vector &b) {   Vector r;   for (int x=0; x<VECLEN; ++x)     if (a.v[x] > b.v[x])       r.v[x] = a.v[x];     else       r.v[x] = b.v[x];   return(r); }

EXAMPLES

~p0; a = VectorMax(b,c); On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 } On Exit: a  = { 9 9 6 5 4 5 9 9 } !p0; a = VectorMax(b,c); On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 } On Exit: a  = { 0 0 6 5 4 5 0 0 }

Some of the following instructions test and generate predicate vectors, setting processor processor status flages to reflect the results. If the instruction generating the predicates is itself predicated, then the flags reflect the status of the active elements only. Each instruction may set some or all of the flags, and different instructions set different flags.

 (ZF) NONE - Set if no active elements of the vector  are true  (PF) ALL - Set if all of the active elements of the  vector are true  (SF) FIRST - Set if the first actuve element of the  vector is true  (OF) LAST - Set if the last active element of the  vector is true  (CF) CARRY - Set if the last active element of  GeneratePredicates( ) output is true   ANY - Logical inverse of NONE (!ZF)   ABOVE - This condition is calculated from  ((CF==0) && (ZF==0)) VectorTest

This instruction tests the input predicate vector and sets the processor status flags accordingly. The interface for this instruction is:

 void VectorTest(Vector &p)  Flags: ZF - Set if no active elements are true. Cleared otherwise. SF/OF/PF - Indicates whether the First/Last/All active elements of the result are true. VectorEQ

This instruction compares active vector elements and returns a result vector indicating whether the elements of the first parameter are equal to elements of the second parameter. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Flags: ZF - Set if no active elements are true. Cleared otherwise. SF/OF/PF - Indicates whether the First/Last/All active elements of the result are true. Vector VectorEQ (const Vector &ob, const Vector &val) {   Vector result;   for (int x=0; x<VECLEN; ++x)       result.v[x] = (ob.v[x] == val.v[x]);   return(result); }

EXAMPLES

 ~p0; a = (b == c);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 }  On Exit: a  = { 9 9 0 0 1 0 9 9 }  !p0; a = (b == c);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 }  On Exit: a  = { 0 0 0 0 1 0 0 0 } VectorGT

This instruction compares active vector elements and returns a result vector indicating whether the elements of the first parameter are greater-than elements of the second parameter. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Flags: ZF - Set if no active elements are true. Cleared otherwise. SF/OF/PF - Indicates whether the First/Last/All active elements of the result are true. Vector VectorGT (const Vector &ob, const Vector &val) {   Vector result;   for (int x=0; x<VECLEN; ++x)       result.v[x] = (ob.v[x] > val.v[x]);   return(result); }

EXAMPLES

 ~p0; a = (b > c);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 }  On Exit: a  = { 9 9 1 1 0 0 9 9 }  !p0; a = (b > c);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 }  On Exit: a  = { 0 0 1 1 0 0 0 0 } VectorGE

This instruction compares active vector elements and returns a result vector indicating whether the elements of the first parameter are greater-than or equal-to elements of the second parameter. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Flags: ZF - Set if no active elements are true. Cleared otherwise. SF/OF/PF - Indicates whether the First/Last/All active elements of the result are true. Vector VectorGE (const Vector &ob, const Vector &val) {   Vector result;   for (int x=0; x<VECLEN; ++x)       result.v[x] = (ob.v[x] >= val.v[x]);   return(result); }

EXAMPLES

 ~p0; a = (b >= c);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 }  On Exit: a  = { 9 9 1 1 1 0 9 9 }  !p0; a = (b >= c);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 }  On Exit: a  = { 0 0 1 1 1 0 0 0 } VectorNEQ

This instruction compares active vector elements and returns a result vector indicating whether the elements of the first parameter are non-equal to elements of the second parameter. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. This implementation of the instruction takes the result vector as an input and performs predication explicitly.

Flags: ZF - Set if no active elements are true. Cleared otherwise. SF/OF/PF - Indicates whether the First/Last/All active elements of the result are true. Vector VectorNEQ (const Vector &ob, const Vector &val) {   Vector result;   for (int x=0; x<VECLEN; ++x)       result.v[x] = (ob.v[x] != val.v[x]);   return(result); }

EXAMPLES

 ~p0; a = (b != c);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 }  On Exit: a  = { 9 9 1 1 0 1 9 9 }  !p0; a = (b != c);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 8 7 6 5 4 3 2 1 } c  = { 0 1 2 3 4 5 6 7 }  On Exit: a  = { 0 0 1 1 0 1 0 0 } Continue

This instruction logically negates active vector elements. Inactive elements either remain unmodified, or are forced to zero, depending on the nature of the predication. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Flags: ZF - Set if no active elements are true. Cleared otherwise. SF/OF/PF - Indicates whether the First/Last/All active elements of the result are true. Vector Continue(Vector &p) {   Vector r;   for (int x=0; x<VECLEN; ++x)       r.v[x] = !p.v[x];   return(r); }

EXAMPLES

 ~p0; a = Continue(b);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 0 −2 −1 0 1 2 3 0 }  On Exit: a  = { 9 9 0 1 0 0 9 9 }  !p0; a = Continue(b);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 0 −2 −1 0 1 2 3 0 }  On Exit: a  = { 0 0 0 1 0 0 0 0 } Break

This instruction returns a vector containing ones in all positions before the first non-zero element position of its input, and zeroes all other positions. Predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

 Flags: ZF - Set if no active elements are true. Cleared otherwise. SF/OF/PF - Indicates whether the First/Last/All active elements of the result are true. Vector Break(Vector &p) {   Vector r = 0;   for (int x=0; x<VECLEN; ++x)   {       if (p.v[x])        break;       r.v[x] = 1;   }   return(r); }

EXAMPLES

 ~p0; a = Break(b);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 0 1 0 0 1 0 0 0 }  On Exit: a  = { 9 9 1 1 0 0 9 9 }  !p0; a = Break(b);  On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 0 1 0 0 1 0 0 0 }  On Exit: a  = { 0 0 1 1 0 0 0 0 } PreBreak

This instruction returns a vector containing zeroes in all positions after the first non-zero element position of its input, and ones in all other positions. Predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Flags: ZF - Set if no active elements are true. Cleared otherwise. SF/OF/PF - Indicates whether the First/Last/All active elements of the result are true. Vector PreBreak(Vector &p) {    Vector r = 0;    for (int x=0; x<VECLEN; ++x)    {      r.v[x] = 1;      if (p.v[x])         break;    }    return(r); }

EXAMPLES

   ~p0; a = PreBreak(b);    On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 0 1 0 0 1 0 0 0 }    On Exit: a = { 9 9 1 1 1 0 9 9 }    !p0; a  = PreBreak(b);    On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 0 1 0 0 1 0 0 0 }    On Exit: a = { 0 0 1 1 1 0 0 0 } Remaining

This instruction sets all elements after the last non-zero element to 1, and all other elements to zero. An input vector of all zero elements returns all ones, and a vector of all non-zero returns all zeroes. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Flags: ZF - Set if no active elements are true. Cleared otherwise. SF/OF/PF - Indicates whether the First/Last/All active elements of the result are true. Vector Remaining(Vector &p) {    Vector r = 0;    int x;    for (x=VECLEN−1; x>=0; −−x) // Locate last    active predicate in input      if (p.v[x])         break;    for (++x; x<VECLEN; ++x)      r.v[x] = 1;    return(r); }

EXAMPLES

   ~p0; a = Remaining(b);    On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 0 1 0 1 0 0 1 0 }    On Exit: a = { 9 9 0 0 1 1 9 9 }    !p0; a = Remaining(b);    On Entry: p0 = { 0 0 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 0 1 0 1 0 0 1 0 }    On Exit: a = { 0 0 0 0 1 1 0 0 } GeneratePredicates

This instruction takes a dependency index vector, DIV, and generates predicates corresponding to the next group of elements that may safely be processed in parallel, given the previous group that was processed which is indicated by prev. If no elements of prev are active, predicates are generated for the first group of elements that may safely be processed in parallel. If prev indicates that the final elements of the vector have been processed, then a result vector of inactive predicates is returned. The definition of GeneratePredicates follows. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. (Note that GeneratePredicates uses the destination register as one of its inputs.)

Flags: ZF - Set if no active elements are true. Cleared otherwise. CF - Set if the last active element is true. Cleared otherwise. Vector GeneratePredicates(Vector &prev, Vector &index) {    Vector r = 0;    int x, pos;    for (x=VECLEN−1; x>=0; −−x)      if (prev.v[x])         break;    for (x=VECLEN−1; x>=0; −−x)      if(prev.v[x])         break;    pos = x+1; //start at next position    for(++x; x<VECLEN; ++x)    {      if(index.v[x]>pos) // compare DIV (1-      based) value to position (0-based)         break;      r.v[x] = 1;    }    SetGeneratePredicatesFlags(r);    return(r); }

EXAMPLES

   ~p0; p1 = GeneratePredicates(p1,ix);    On Entry: p0 = { 1 1 1 1 1 1 1 0 } p1 = { 0 0 0 0 0 0 0 0 } ix = { 0 0 0 2 1 3 4 0 }    On Exit1: p1 = { 1 1 1 0 0 0 0 0 }    On Entry: p1 = { 1 1 1 0 0 0 0 0 }    On Exit2: p1 = { 0 0 0 1 1 1 0 0 }    On Entry: p1 = { 0 0 0 1 1 1 0 0 }    On Exit3: p1 = { 0 0 0 0 0 0 1 0 }    !p0; p1 = GeneratePredicates(p1,ix);    On Entry: p0 = { 1 1 1 1 1 1 1 0 } p1 = { 0 0 0 0 0 0 0 0 } ix = { 0 0 0 2 1 3 4 0 }    On Exit1: p1 = { 1 1 1 0 0 0 0 0 }    On Entry: p1 = { 1 1 1 0 0 0 0 0 }    On Exit2: p1 = { 0 0 0 1 1 1 0 0 }    On Entry: p1 = { 0 0 0 1 1 1 0 0 }    On Exit3: p1 = { 0 0 0 0 0 0 1 0 } CheckHazardP

This instruction examines two vectors of memory addresses (or array indices), corresponding to two memory operations, for potential data dependencies through memory. The vector first holds addresses for the first memory operation, and the vector second holds addresses for the second operation. The predicate pred indicates which elements of second are to be operated upon. This instruction checks for addresses that overlap between each element of first and lower-numbered elements of second. In the case of multiple matches, only the highest-numbered position is recorded. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

The 1-based element position corresponding to the iteration that generates the data that is depended upon is stored in the destination vector at the element position corresponding to the iteration that is dependent upon the data. If no data dependency exists, a zero is stored in the destination vector at the element position corresponding to the iteration that does not have the dependency. Variants of this instruction should account for overlap between various sizes of data types.

The CheckHazardP instruction only supports zeroing predication. Non-zeroing predication is not allowed.

Vector CheckHazardP(Vector &first, Vector &second, Vector &p) {    Vector result = 0;    int x,y;    for (x=0; x<VECLEN; ++x)      for (y=0; y<x; ++y)        if (p.v[y])         if (OVERLAP(first.v[x], second.v[y]))             result.v[x] = y + 1;    return(result); }

EXAMPLES

   !p0; a = CheckHazardP(b,c,p1);    On Entry: p0 = { 1 1 1 1 1 1 0 0 } a = { 9 9 9 9 9 9 9 9 } b = { 1 2 1 2 2 1 5 6 } c = { 1 1 2 2 4 5 6 7 } p1 = { 1 1 0 1 1 1 1 1 }    On Exit: a = { 0 0 2 0 4 2 9 9 } CheckHazardPx

This instruction examines two vectors of memory addresses (or array indices), corresponding to two memory operations, for potential data dependencies through memory. The vector first holds addresses for the first memory operation, and vector second holds addresses for the second operation. The predicate pred indicates which elements of second are to be operated upon. This instruction checks for addresses that overlap between each element of first, and lesser-or-equal-numbered elements of second. In the case of multiple matches, only the highest-numbered position is recorded. In the case of a match against an equal-numbered element position, the dependency is recorded in the next-highest position in the result. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

The 1-based element position corresponding to the iteration that generates the data that is depended upon is stored in the destination vector at the element position corresponding to the iteration that is dependent upon the data. If no data dependency exists, a zero is stored in the destination vector at the element position corresponding to the iteration that does not have the dependency. Variants of this instruction should account for overlap between various sizes of data types.

The CheckHazardPX instruction only supports zeroing predication. Non-zeroing predication is not allowed.

Vector CheckHazardPx(Vector &first, Vector &second, Vector &p) {    Vector result = 0;    int x,y;    for (x=1; x<VECLEN; ++x)    {       for (y=0; y<x; ++y)          if (p.v[y])             if (OVERLAP(first.v[x],      second.v[y]))               result.v[x] = y + 1;          if ((OVERLAP(first.v[x−1], second.v[x−          1]) && p.v[x−1]))             result.v[x] = x;    }    return(result); }

EXAMPLES

   !p0; a = CheckHazardPx(b,c,p1);    On Entry: p0 = { 1 1 1 1 1 1 1 0 } a = { 9 9 9 9 9 9 9 9 } b = { 1 1 2 2 5 6 3 6 } c = { 1 2 2 3 4 5 6 6 } p1 = { 0 1 1 1 1 1 1 1 }    On Exit: a = { 0 0 2 3 0 0 4 0 } ConditionalStop

This instruction takes the scalar parameter mode, which indicates any number of four possible transitions between true and false values of adjacent elements in predicate p that imply data dependencies. The parameter mode is a 4-bit field, the bits of which are defined as follows:

-   -   kTF—Implies a loop-carried dependency from an iteration for         which the predicate is true, to the subsequent iteration for         which the value of the predicate is false.     -   kFF—Implies a loop-carried dependency from an iteration for         which the predicate is false, to the subsequent iteration for         which the value of the predicate is false.     -   kFT—Implies a loop-carried dependency from an iteration for         which the predicate is false, to the subsequent iteration for         which the value of the predicate is true.     -   kTT—Implies a loop-carried dependency from an iteration for         which the predicate is true, to the subsequent iteration for         which the value of the predicate is true.

The 1-based (i.e., considering the vector as starting with element “1”) element position corresponding to the iteration that generates the data that is depended upon is stored in the destination vector at the element position corresponding to the iteration that depends on the data. If no data dependency exists, a value of 0 is stored in the destination vector at that element.

Vector ConditionalStop(Vector &p, int mode) {    Vector r = 0;    for (int x=1; x<VECLEN; ++x) // Skip the first    element    {       if (p.v[x−1] == 0 && p.v[x] == 0)       {          if (mode & kFF)             r.v[x] = x;       }       else if (p.v[x−1] == 0 && p.v[x] == 1)       {          if (mode & kFT)             r.v[x] = x;       }       else if (p.v[x−1] == 1 && p.v[x] == 0)       {          if (mode & kTF)             r.v[x] = x;       }       else       {          if (mode & kTT)             r.v[x] = x;       }    }    return(r); }

EXAMPLES

   ~p0; a = ConditionalStop(b, kTF|kFT);    On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 0 1 0 1 1 0 1 0 }    On Exit: a  = { 9 9 0 3 0 5 9 9 }    !p0; a = ConditionalStop(b, kTF|kFT);    On Entry: p0 = { 0 0 1 1 1 1 0 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 0 1 0 1 1 0 1 0 }    On Exit: a  = { 0 0 0 3 0 5 0 0 } PropagatePostT

This instruction propagates the value of active elements in s, as determined by predicate p, to subsequent inactive elements in the destination. Active elements remain unchanged, and any inactive elements that precede the first active element also remain unchanged. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that the PropagatePostT uses the destination register as one if its inputs.

Vector PropagatePostT(Vector &d, Vector &s, Vector &p) {    Vector r = 0;    int x,y;    for (x=0; x<VECLEN; ++x) // Until first active    predicate, preserve dest    {       y = x;       r.v[x] = d.v[x];       if (p.v[x])          break;    }    for (++x; x<VECLEN; ++x)       if (p.v[x])       {          r.v[x] = d.v[x]; // While predicate ==          1, preserve dest          y = x;       }       else          r.v[x] = s.v[y]; // While predicate ==          0, copy final from source    return(r); }

EXAMPLES

   ~p0; a = PropagatePostT(a,b,p1);    On Entry: p0 = {  0 1 1 1 1 1 1 1 } a  = {  8 9 A B C D E F } b  = {  0 1 2 3 4 5 6 7 } p1 = {  0 0 1 1 0 0 1 0 }    On Exit: a  = {  8 9 A B 3 3 E 6 }    !p0; a = PropagatePostT(a,b,p1);    On Entry: p0 = {  0 1 1 1 1 1 1 1 } a  = {  8 9 A B C D E F } b  = {  0 1 2 3 4 5 6 7 } p1 = {  0 0 1 1 0 0 1 0 }    On Exit: a  = {  0 9 A B 3 3 E 6 } PropagatePriorF

This instruction propagates the value of the inactive elements of src, as determined by predicate p, into subsequent active elements. Inactive elements are copied from src to the destination. If the first element of predicate is active, then the last element of src is propagated to that position. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector PropagatePriorF(Vector &src, Vector &p) {    Vector r = 0;    int x,y;    y = VECLEN − 1; // y is position of element to    propagate    for (x=0; x<VECLEN; ++x) // Destination unchanged    until first active predicate    {       if (gPred.v[x] && p.v[x])          break;       r.v[x] = src.v[x];       y = x;    }    for (; x<VECLEN; ++x)    {       if (gPred.v[x] && p.v[x])       {          r.v[x] = src.v[y]; // Propagate on          active predicates       }       else       {          r.v[x] = src.v[x]; // Copy on inactive          predicates          y = x;       }    }    return(r); }

EXAMPLES

 ~p0; a = PropagatePriorF(b,p1);  On Entry: p0 = { 0 1 1 1 1 1 1 0 } a = { 9 9 9 9 9 9 9 9 } b = { 1 2 3 4 5 6 7 8 } p1 = { 0 0 1 1 0 0 1 0 }  On Exit: a = { 9 2 2 2 5 6 6 9 }  On Entry: p0 = { 1 1 1 1 1 1 1 0 } a = { 9 9 9 9 9 9 9 9 } b = { 1 2 3 4 5 6 7 8 } p1 = { 1 1 0 1 0 0 1 1 }  On Exit: a = { 8 8 3 3 5 6 6 9 }  !p0; a = PropagatePriorF(b,p1);  On Entry: p0 = { 0 1 1 1 1 1 1 0 } a = { 9 9 9 9 9 9 9 9 } b = { 1 2 3 4 5 6 7 8 } p1 = { 0 0 1 1 0 0 1 0 }  On Exit: a = { 0 2 2 2 5 6 6 0 }  On Entry: p0 = { 1 1 1 1 1 1 1 0 } a = { 9 9 9 9 9 9 9 9 } b = { 1 2 3 4 5 6 7 8 } p1 = { 1 1 1 1 0 0 1 1 }  On Exit: a = { 8 8 3 3 5 6 6 0 } CopyPropagate

This instruction copies active elements, as determined by p, from src to the destination register. Active elements are propagated into inactive elements in the process. Any initial inactive elements remain unchanged in the destination. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that CopyPropagate uses the destination register as one of its inputs.

Vector CopyPropagate(Vector &dest, Vector &src, Vector &p) {   Vector r;   int x,y;   y = 0;   for (x=0; x<VECLEN; ++x) // Find first active   pred, dest unchanged     if (p.v[x] && gPred.v[x])       break;     else     {       r.v[x] = dest.v[x];       y = x;     }   for (; x<VECLEN; ++x) // If active: copy. If   inactive: propagate   {     if (p.v[x] && gPred.v[x])     {       r.v[x] = src.v[x];       y = x;     }     else       r.v[x] = src.v[y];   }   return(r); }

EXAMPLES

 ~p0; a = CopyPropagate(a,b,p1);  On Entry: p0 = { 0 1 1 1 1 1 1 1 } a = { 9 9 9 9 9 9 9 9 } b = { 1 2 3 4 5 6 7 8 } p1 = { 0 0 1 1 0 0 1 0 }  On Exit: a = { 9 9 3 4 4 4 7 7 }  !p0; a = CopyPropagate(a,b,p1);  On Entry: p0 = { 0 1 1 1 1 1 1 1 } a = { 9 9 9 9 9 9 9 9 } b = { 1 2 3 4 5 6 7 8 } p1 = { 0 0 1 1 0 0 1 0 }  On Exit: a = { 0 9 3 4 4 4 7 7 } ShiftInRightP

This instruction shifts vector elements to the right, or propagates active values, as determined by input predicate p. The first active element receives the input scalar j. The resulting vector is stored to the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector ShiftInRightP(int j, const Vector &v, int &p) {   Vector r = 0;   int x;   r = v;   for(x=0; x<VECLEN; ++x)     if(gPred.v[x])       break;   r.v[x] = j;   for (++x; x<VECLEN; ++x)   {     if (gPred.v[x] && p.v[x−1])       r.v[x] = v.v[x−1];     else if (gPred.v[x])       r.v[x] = r.v[x−1];     else       r.v[x] = v.v[x−1];   }   return(r); }

EXAMPLES

 ~p0; a = ShiftInRightP(j,b,p1);  On Entry: j = 9 p0 = { 0 0 1 1 1 1 1 1 } a = { 1 2 3 4 5 6 7 8 } p1 = { 0 1 1 1 0 0 1 1 }  On Exit: a = { 1 2 9 3 4 4 4 7 }  !p0; a = ShiftInRightP(j,b,p1);  On Entry: j = 9 p0 = { 0 0 1 1 1 1 1 1 } a = { 1 2 3 4 5 6 7 8 } p1 = { 0 1 1 1 0 0 1 1 }  On Exit: a = { 0 0 9 3 4 4 4 7 } ShiftInRight

This instruction shifts vector elements to the right, or propagates active values, as determined by input predicate p. The first element receives the input scalar j. The resulting vector is stored to the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector ShiftInRight(int j, const Vector &v, int &p) {   Vector r = 0;   int x;   r.v[0] = j;   for (x=1; x<VECLEN; ++x)   {     if (gPred.v[x] && p.v[x−1])       r.v[x] = v.v[x−1];     else if (gPred.v[x])       r.v[x] = r.v[x−1];     else       r.v[x] = v.v[x−1];   }   return(r); }

EXAMPLES

 ~p0; a = ShiftInRightP(j,b,p1);  On Entry: j = 9 p0 = { 0 0 1 1 1 1 1 1 } a = { 1 2 3 4 5 6 7 8 } p1 = { 0 1 1 1 0 0 1 1 }  On Exit: a = { 1 2 9 3 4 4 4 7 }  !p0; a = ShiftInRightP(j,b,p1);  On Entry: j = 9 p0 = { 0 0 1 1 1 1 1 1 } a = { 1 2 3 4 5 6 7 8 } p1 = { 0 1 1 1 0 0 1 1 }  On Exit: a = { 0 0 9 3 4 4 4 7 } SelectLast

Use of the ShiftInRightP instruction often requires that the shifted-out element be captured to be shifted in during the next pass. Normally this is accomplished using a simple scalar cast prior to the use of ShiftInRightP. In cases where the shifted-out value may come from more than one vector under control of predication, the SelectLast instruction is used to capture the last element from one of two vectors. Note that the final element for which p0 is set determines which element position p1 is to be evaluated for.

int SelectLast(cont Vector &v1, const Vector &v2, const Vector &p) {   Vector r = 0;   int x;   for (x=VECLEN−1; x>=0; −−x)     if (gPred.v[x])       break;   if (x >= 0)     if (p.v[x])       r = v2.v[x];     else       r = v1.v[x];   return(r); }

EXAMPLES

 ~p0; a = SelectLast (a,b,p1);  On Entry: j = 9 p0 = { 1 1 0 0 1 1 0 0 } a = { 1 2 3 4 5 6 7 8 } b = { 9 8 7 6 5 4 3 2 } p1 = { 0 0 1 1 1 0 0 1 }  On Exit: a = 6  !p0; a = SelectLast (a,b,p1);  On Entry: j = 9 p0 = { 1 1 0 0 1 1 0 0 } a = { 1 2 3 4 5 6 7 8 } b = { 9 8 7 6 5 4 3 2 } p1 = { 0 0 1 1 1 1 0 1 }  On Exit: a = 4 ShiftRight

This instruction shift vector elements to the right, populating the first element with the input scalar j. The resulting vector is stored to the destination register.

Vector ShiftInRight(int j, const Vector &v, int &p) {   Vector r = 0;   int x;   r.v[0] = j;   for (++x; x<VECLEN; ++x)   {     r.v[x] = v.v[x−1];   }   return(r); }

EXAMPLES

 ~p0; a = ShiftRight(j,b,p1);  On Entry: j = 9 p0 = { 1 1 1 0 0 1 1 1 } a = { A A A A A A A A } b = { 1 2 3 4 5 6 7 8 }  On Exit: a = { 9 1 2 A A 5 6 7 }  !p0; a = ShiftRight(j,b,p1);  On Entry: j = 9 p0 = { 1 1 1 0 0 1 1 1 } a = { A A A A A A A A } b = { 1 2 3 4 5 6 7 8 }  On Exit: a = { 9 1 2 0 0 5 6 7 } IncrPropagate1

Using the value of the first active element in s as a basis, this instruction cumulatively increments this basis for every active element specified by predicate p. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being incremented into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector IncrPropagate1(Vector &s, Vector &p) {   Vector r;   int x,v;   for (x=0; x<VECLEN; ++x)   {     if (gPred.v[x] && p.v[x])     {       v = s.v[x];       break;     }     r.v[x] = s.v[x];   }   for (; x<VECLEN; ++x)   {     r.v[x] = v;     if (gPred.v[x] && p.v[x])       ++v;   }   return(r); }

EXAMPLES

 ~p0; a = IncrPropagate1(b,p1);  On Entry: p0 = { 1 1 1 1 1 1 1 0 } a = { 9 9 9 9 9 9 9 9 } b = { 3 3 3 3 3 3 3 3 } p1 = { 0 1 1 0 0 1 1 0 }  On Exit: a = { 3 3 4 5 5 5 6 9 }  !p0; a = IncrPropagate1(b,p1);  On Entry: p0 = { 1 1 1 1 1 1 1 0 } a = { 9 9 9 9 9 9 9 9 } b = { 3 3 3 3 3 3 3 3 } p1 = { 0 1 1 0 0 1 1 0 }  On Exit: a = { 3 3 4 5 5 5 6 0 } IncrPropagate2

Using the value of the first active element in s as a basis, this instruction cumulatively increments this basis for every active element specified by predicate p. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being incremented into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector IncrPropagate2(Vector &s, Vector &p) {   Vector r;   int x,v;   for (x=0; x<VECLEN; ++x)   {     if (gPred.v[x] && p.v[x])     {       v = s.v[x];       break;     }     r.v[x] = s.v[x];   }   for (; x<VECLEN; ++x)   {     if (gPred.v[x] && p.v[x])       ++v;     r.v[x] = v;   }   return(r); }

EXAMPLES

 ~p0; a = IncrPropagate2(b,p1);  On Entry: p0 = { 1 1 1 1 1 1 1 0 } a = { 9 9 9 9 9 9 9 9 } b = { 3 3 3 3 3 3 3 3 } p1 = { 0 1 1 0 0 1 1 0 }  On Exit: a = { 3 4 5 5 5 6 7 9 }  !p0; a = IncrPropagate2(b,p1); On Entry: p0 = { 1 1 1 1 1 1 1 0 } a = { 9 9 9 9 9 9 9 9 } b = { 3 3 3 3 3 3 3 3 } p1 = { 0 1 1 0 0 1 1 0 }  On Exit: a = { 3 4 5 5 5 6 7 0 } DecrPropagate1

Using the value of the first active element in s as a basis, this instruction cumulatively decrements this basis for every active element specified by predicate p. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being decremented into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector DecrPropagate1(Vector &s, Vector &p) {  Vector r;  int x,v;  for (x=0; x<VECLEN; ++x)  {   if (gPred.v[x] && p.v[x])   {    v = s.v[x];    break;   }   r.v[x] = s.v[x];  }  for (; x<VECLEN; ++x)  {   r.v[x] = v;   if (gPred.v[x] && p.v[x])    −−v;  }  return(r); }

EXAMPLES

  ~p0; a  = DecrPropagate1(b,p1);   On Entry: p0 = { 1 1 1 1 1 1 1 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 7 7 7 7 7 7 7 7 } p1 = { 0 1 1 0 0 1 1 0 }   On Exit: a  = { 7 7 6 5 5 5 4 9 }   !p0; a  = DecrPropagate1(b,p1);   On Entry: p0 = { 1 1 1 1 1 1 1 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 7 7 7 7 7 7 7 7 } p1 = { 0 1 1 0 0 1 1 0 }   On Exit: a  = { 7 7 6 5 5 5 4 0 } DecrPropagate2

Using the value of the first active element in s as a basis, this instruction cumulatively decrements this basis for every active element specified by predicate p. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being decremented into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction.

Vector DecrPropagate2(Vector &s, Vector &p) {  Vector r;  int x,v;  for (x=0; x<VECLEN; ++x)  {   if (gPred.v[x] && p.v[x])   {    v = s.v[x];    break;   }   r.v[x] = s.v[x];  }  for (; x<VECLEN; ++x)  {   if (gPred.v[x] && p.v[x])    −−v;   r.v[x] = v;  }  return(r); }

EXAMPLES

  ~p0; a  = DecrPropagate2(b,p1);   On Entry: p0 = { 1 1 1 1 1 1 1 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 7 7 7 7 7 7 7 7 } p1 = { 0 1 1 0 0 1 1 0 }   On Exit: a  = { 7 6 5 5 5 4 3 9 }   !p0; a  = DecrPropagate2(b,p1);   On Entry: p0 = { 1 1 1 1 1 1 1 0 } a  = { 9 9 9 9 9 9 9 9 } b  = { 7 7 7 7 7 7 7 7 } p1 = { 0 1 1 0 0 1 1 0 }   On Exit: a  = { 7 6 5 5 5 4 3 0 } RunningSum1P

Using the value of the first active element in a as a basis, this instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that the RunningSum1P instruction uses the destination register as one of its inputs.

Vector RunningSum1P(const Vector &a, const Vector &b, const Vector &p) {  Vector r;  int s,base,x;  base = s = 0;  for (x=0; x<VECLEN; ++x)  {   if ((gPred.v[x]) && (p.v[x] ))   {    base = a.v[x];    break;   }   else    r.v[x] = a.v[x];  }  for (; x<VECLEN; ++x)  {   r.v[x] = base + s;   if ((gPred.v[x]) && (p.v[x] ))    s += b.v[x];  }  return(r); }

EXAMPLES

  ~p0; a  = RunningSum1P(a,b,p1);   On Entry: p0 = { 1 1 1 1 1 0 1 0 } a  = { 0 1 2 3 4 5 6 7 } b  = { 1 2 3 4 5 6 7 8 } p1 = { 1 0 1 0 1 1 1 0 }   On Exit: a  = { 0 1 1 4 4 5 9 7 }   !p0; a  = RunningSum1P(a,b,p1);   On Entry: p0 = { 1 1 1 1 1 0 1 0 } a  = { 0 1 2 3 4 5 6 7 } b  = { 1 2 3 4 5 6 7 8 } p1 = { 1 0 1 0 1 1 1 0 }   On Exit: a  = { 0 1 1 4 4 0 9 0 } RunningSum2P

Using the value of the first active element in a as a basis, this instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that the RunningSum2P instruction uses the destination register as one of its inputs.

Vector RunningSum2P(const Vector &a, const Vector &b, const Vector &p) {  Vector r;  int s,base,x;  base = s = 0;  for (x=0; x<VECLEN; ++x)  {   if ((gPred.v[x]) && (p.v[x] ))   {    base = a.v[x];    break;   }   else    r.v[x] = a.v[x];  }  for (; x<VECLEN; ++x)  {   if ((gPred.v[x]) && (p.v[x] ))    s += b.v[x];   r.v[x] = base + s;  }  return(r); }

EXAMPLES

  ~p0; a  = RunningSum2P(a,b,p1);   On Entry: p0 = { 1 1 1 1 1 0 1 0 } a  = { 0 1 2 3 4 5 6 7 } b  = { 1 2 3 4 5 6 7 8 } p1 = { 1 0 1 0 1 1 1 0 }   On Exit: a  = { 1 1 4 4 9 5 16 7 }   !p0; a  = RunningSum2P(a,b,p1);   On Entry: p0 = { 1 1 1 1 1 0 1 0 } a  = { 0 1 2 3 4 5 6 7 } b  = { 1 2 3 4 5 6 7 8 } p1 = { 1 0 1 0 1 1 1 0 }   On Exit: a  = { 1 1 4 4 9 0 16 0 } RunningShift1R

Using the value of the first active element in a as a basis, this instruction right-shifts this basis by the cumulative number of bits specified by active elements in b. Predicate p determines which elements participate in the accumulation of shift-counts. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being shifted into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that the RunningShift1R instruction uses the destination register as one of its inputs.

Vector RunningShift1R(const Vector &a, const Vector &b, const Vector &p) {  Vector r;  int s,base,x;  base = s = 0;  for (x=0; x<VECLEN; ++x)  {   if (gPred.v[x] && p.v[x])   {    base = a.v[x];    break;   }   else    r.v[x] = a.v[x];  }  for (; x<VECLEN; ++x)  {   r.v[x] = base >> s;   if (gPred.v[x] && p.v[x])    s += b.v[x];  }  return(r); }

EXAMPLES

  ~p0; a  = RunningShift1R(a,b,p1);   On Entry: p0 = {  1 1 1 1 1 1 1 0 } a  = { 63 63 63 63 63 63 63 63 } b  = {  0 1 1 2 2 3 3 4 } p1 = {  0 1 1 0 0 1 1 0 }   On Exit: a  = { 64 64 32 16 16 16 2 64 }   !p0; a  = RunningShift1R(a,b,p1);   On Entry: p0 = {  1 1 1 1 1 1 1 0 } a  = { 63 63 63 63 63 63 63 63 } b  = {  0 1 1 2 2 3 3 4 } p1 = {  0 1 1 0 0 1 1 0 }   On Exit: a  = { 64 64 32 16 16 16 2 0 } RunningShift2R

Using the value of the first active element in a as a basis, this instruction right-shifts this basis by the cumulative number of bits specified by active elements in b. Predicate p determines which elements participate in the accumulation of shift-counts. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being shifted into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that the RunningShift2R instruction uses the destination register as one of its inputs.

Vector RunningShift2R(const Vector &a, const Vector &b, const Vector &p) {  Vector r;  int s,base,x;  base = s = 0;  for (x=0; x<VECLEN; ++x)  {   if (gPred.v[x] && p.v[x])   {    base = a.v[x];    break;   }   else    r.v[x] = a.v[x];  }  for (; x<VECLEN; ++x)  {   if (gPred.v[x] && p.v[x])    s += b.v[x];   r.v[x] = base >> s;  }  return(r); }

EXAMPLES

  ~p0; a  = RunningShift2R(a,b,p1);   On Entry: p0 = {  1 1 1 1 1 1 1 0 } a  = { 64 64 64 64 64 64 64 64 } b  = {  0 1 1 2 2 3 3 4 } p1 = {  0 1 1 0 0 1 1 0 }   On Exit: a  = { 64 32 16 16 16 2 0 64 }   !p0; a  = RunningShift2R(a,b,p1);   On Entry: p0 = {  1 1 1 1 1 1 1 0 } a  = { 64 64 64 64 64 64 64 64 } b  = {  0 1 1 2 2 3 3 4 } p1 = {  0 1 1 0 0 1 1 0 }   On Exit: a  = { 64 32 16 16 16 2 0 0 } RunningShift1L

Using the value of the first active element in a as a basis, this instruction left-shifts this basis by the cumulative number of bits specified by active elements in b. Predicate p determines which elements participate in the accumulation of shift-counts. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being shifted into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that the RunningShift1L instruction uses the destination register as one of its inputs.

Vector RunningShift1L(const Vector &a, const Vector &b, const Vector &p) {  Vector r;  int s,base,x;  base = s = 0;  for (x=0; x<VECLEN; ++x)  {   if (gPred.v[x] && p.v[x])   {    base = a.v[x];    break;  }  else    r.v[x] = a.v[x];  }  for (; x<VECLEN; ++x)  {   r.v[x] = base << s;   if (gPred.v[x] && p.v[x])    s += b.v[x];  }  return(r); }

EXAMPLES

  ~p0; a  = RunningShift1L(a,b,p1);   On Entry: p0 = { 1 1 1 1 1 1 1 0 } a  = { 0 1 2 3 4 5 6 7 } b  = { 0 1 1 1 2 2 2 3 } p1 = { 0 1 1 0 0 1 1 0 }   On Exit: a  = { 0 1 2 4 4 4 16 7 }   !p0; a  = RunningShift1L(a,b,p1);   On Entry: p0 = { 1 1 1 1 1 1 1 0 } a  = { 0 1 2 3 4 5 6 7 } b  = { 0 1 1 1 2 2 2 3 } p1 = { 0 1 1 0 0 1 1 0 }   On Exit: a  = { 0 1 2 4 4 4 16 0 } RunningShift2L

Using the value of the first active element in a as a basis, this instruction left-shifts this basis by the cumulative number of bits specified by active elements in b. Predicate p determines which elements participate in the accumulation of shift-counts. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being shifted into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that the RunningShift2L instruction uses the destination register as one of its inputs.

Vector RunningShift2L(const Vector &a, const Vector &b, const Vector &p) {  Vector r;  int s,base,x;  base = s = 0;  for (x=0; x<VECLEN; ++x)  {   if (gPred.v[x] && p.v[x])   {    base = a.v[x];    break;  }  else    r.v[x] = a.v[x];  }  for (; x<VECLEN; ++x)  {   if (gPred.v[x] && p.v[x])    s += b.v[x];   r.v[x] = base << s;  }  return(r); }

EXAMPLES

  ~p0; a = RunningShift2L(a,b,p1);   On Entry: p0 = { 1  1  1  1  1   1   1  0 } a = { 0  1  2  3  4   5   6  7 } b = { 0  1  1  1  2   2   2  3 } p1 = { 0  1  1  0  0   1   1  0 }   On Exit: a = { 0  2  4  4  4  16  64  7 }   !p0; a = RunningShift2L(a,b,p1);   On Entry: p0 = { 1  1  1  1  1   1   1  0 } a = { 0  1  2  3  4   5   6  7 } b = { 0  1  1  1  2   2   2  3 } p1 = { 0  1  1  0  0   1   1  0 }   On Exit: a = { 0  2  4  4  4  16  64  0 } RunningMin1P

Using the value of the first active element in a as a basis, the RunningMin1P instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningMin1P uses the destination register as one of its inputs.

Vector RunningMin1P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,x;   s = 0;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))     {       s = a.v[x];       break;     }     else     r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     r.v[x] = s;     if ((gPred.v[x]) && (p.v[x]))       s = MIN(s, b.v[x]);   }   return(r); }

EXAMPLES

  ~p0; a = RunningMin1P(a,b,p1);   On Entry: p0 = { 0 0 1 1 0 1 1 1 } a = { 0 1 D C B A 9 8 } b = { 2 3 4 5 2 5 3 1 } p1 = { 1 0 1 0 0 1 1 0 }   On Exit: a = { 0 1 D 4 B 4 4 3 }   !p0; a = RunningMin1P(a,b,p1);   On Entry: p0 = { 0 0 1 1 0 1 1 1 } a = { 0 1 D C B A 9 8 } b = { 2 3 4 5 2 5 3 1 } p1 = { 1 0 1 0 0 1 1 0 }   On Exit: a = { 0 0 D 4 0 4 4 3 } RunningMin2P

Using the value of the first active element in a as a basis, the RunningMin2P instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningMin2P uses the destination register as one of its inputs.

Vector RunningMin2P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,x;   s = 0;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x]))     {       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x]))       s = MIN(s, b.v[x]);     r.v[x] = s;   }   return(r); }

EXAMPLES

  ~p0; a = RunningMin2P(a,b,p1);   On Entry: p0 = { 0 0 1 1 0 1 1 1 } a = { 0 1 D C B A 9 8 } b = { 2 3 4 5 2 5 3 1 } p1 = { 1 0 1 0 0 1 1 0 }   On Exit: a = { 0 1 4 4 B 4 3 3 }   !p0; a = RunningMin2P(a,b,p1);   On Entry: p0 = { 0 0 1 1 0 1 1 1 } a = { 0 1 D C B A 9 8 } b = { 2 3 4 5 2 5 3 1 } p1 = { 1 0 1 0 0 1 1 0 }   On Exit: a = { 0 0 4 4 0 4 3 3 } RunningMax1P

Using the value of the first active element in a as a basis, the RunningMax1P instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by th e assignment of the result, and should be considered an integral part of this instruction. Note that RunningMax1P uses the destination register as one of its inputs.

Vector RunningMax1P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,x;   s = 0;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x]))     {       s = a.v[x];       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     r.v[x] = s;     if ((gPred.v[x]) && (p.v[x]))       s = MAX(s, b.v[x]);   }   return(r); }

EXAMPLES

  ~p0; a = RunningMax1P(a,b,p1);   On Entry: p0 = { 0  0  1  1  0  1  1  1 } a = { 6  7  2  3  4  5  6  7 } b = { 8  9  1  4  5  6  7  8 } p1 = { 1  0  1  0  1  1  1  0 }   On Exit: a = { 6  7  2  2  4  2  6  7 }   !p0; a = RunningMax1P(a,b,p1);   On Entry: p0 = { 0  0  1  1  0  1  1  1 } a = { 6  7  2  3  4  5  6  7 } b = { 8  9  1  4  5  6  7  8 } p1 = { 1  0  1  0  1  1  1  0 }   On Exit: a = { 0  0  2  2  0  2  6  7 } RunningMax2P

Using the value of the first active element in a as a basis, the RunningMax2P instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after to being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by th e assignment of the result, and should be considered an integral part of this instruction. Note that RunningMax2P uses the destination register as one of its inputs.

Vector RunningMax2P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,x;   s = 0;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x]))     {       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x]))       s = MAX(s, b.v[x]);     r.v[x] = s;   }   return(r); }

EXAMPLES

  ~p0; a = RunningMax2P(a,b,p1);   On Entry: p0 = { 0  0  1  1  0  1  1  1 } a = { 6  7  2  3  4  5  6  7 } b = { 8  9  1  4  5  6  7  8 } p1 = { 1  0  1  0  1  1  1  0 }   On Exit: a = { 6  7  2  2  4  6  7  7 }   !p0; a = RunningMax2P(a,b,p1);   On Entry: p0 = { 0  0  1  1  0  1  1  1 } a = { 6  7  2  3  4  5  6  7 } b = { 8  9  1  4  5  6  7  8 } p1 = { 1  0  1  0  1  1  1  0 }   On Exit: a = { 0  0  2  2  0  6  7  7 } RunningAnd1P

Using the value of the first active element in a as a basis, rgw RunningAnd1P instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningAnd1P uses the destination register as one of its inputs.

Vector RunningAnd1P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,base,x;   base = s = −1;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))     {       base = a.v[x];       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     r.v[x] = base & s;     if ((gPred.v[x]) && (p.v[x]))       s &= b.v[x];   }   return(r); }

EXAMPLES

  ~p0; a = RunningAnd1P(a,b,p1);   On Entry: p0 = { 1   1   1  1  1  0  1  0 } a = { 7  15   0  1  2  3  4  5 } b = { 7  15   7  1  6  1  4  7 } p1 = { 0   1   1  0  1  1  1  0 }   On Exit: a = { 7  15  15  7  7  3  6  5 }   !p0; a = RunningAnd1P(a,b,p1);   On Entry: p0 = { 1   1   1  1  1  0  1  0 } a = { 7  15   0  1  2  3  4  5 } b = { 7  15   7  1  6  1  4  7 } p1 = { 0   1   1  0  1  1  1  0 }   On Exit: a = { 7  15  15  7  7  0  6  0 } RunningAnd2P

Using the value of the first active element in a as a basis, this instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningAnd2P uses the destination register as one of its inputs.

Vector RunningAnd2P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,base,x;   base = s = −1;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))     {       base = a.v[x];       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))       s &= b.v[x];     r.v[x] = base & s;   }   return(r); }

EXAMPLES

  ~p0; a = RunningAnd2P(a,b,p1);   On Entry: p0 = { 1   1  1  1  1  0  1  0 } a = { 7  15  0  1  2  3  4  5 } b = { 7  15  7  1  6  1  4  7 } p1 = { 0   1  1  0  1  1  1  0 }   On Exit: a = { 7  15  7  7  6  3  4  5 }   !p0; a = RunningAnd2P(a,b,p1);   On Entry: p0 = { 1   1  1  1  1  0  1  0 } a = { 7  15  0  1  2  3  4  5 } b = { 7  15  7  1  6  1  4  7 } p1 = { 0   1  1  0  1  1  1  0 }   On Exit: a = { 7  15  7  7  6  0  4  0 } RunningOr1P

Using the value of the first active element in a as a basis, this instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningOr1P uses the destination register as one of its inputs.

Vector RunningOr1P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,base,x;   base = s = 0;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))     {       base = a.v[x];       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     r.v[x] = base | s;     if ((gPred.v[x]) && (p.v[x] ))       s |= b.v[x];   }   return(r); }

EXAMPLES

  ~p0; a = RunningOr1P(a,b,p1);   On Entry: p0 = { 1  1  1  1  1  0  1  0 } a = { 7  1  9  9  9  9  9  9 } b = { 7  2  1  2  3  4  5  6 } p1 = { 0  1  1  0  1  1  1  0 }   On Exit: a = { 7  1  3  3  3  9  3  9 }   !p0; a = RunningOr1P(a,b,p1);   On Entry: p0 = { 1  1  1  1  1  0  1  0 } a = { 7  1  9  9  9  9  9  9 } b = { 7  2  1  2  3  4  5  6 } p1 = { 0  1  1  0  1  1  1  0 }   On Exit: a = { 7  1  3  3  3  0  3  0 } RunningOr2P

Using the value of the first active element in a as a basis, this instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningOr2P uses the destination register as one of its inputs.

Vector RunningOr2P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,base,x;   base = s = 0;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))     {       base = a.v[x];       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))       s |= b.v[x];     r.v[x] = base | s;   }   return(r); }

EXAMPLES

 ~p0; a = RunningOr2P(a,b,p1);  On Entry: p0 = { 1 1 1 1 1 0 1 0 } a = { 7 1 9 9 9 9 9 9 } b = { 7 2 1 2 3 4 5 6 } p1 = { 0 1 1 0 1 1 1 0 }  On Exit: a = { 7 3 3 3 3 9 7 9 }  !p0; a = RunningOr2P(a,b,p1);  On Entry: p0 = { 1 1 1 1 1 0 1 0 } a = { 7 1 9 9 9 9 9 9 } b = { 7 2 1 2 3 4 5 6 } p1 = { 0 1 1 0 1 1 1 0 }  On Exit: a = { 7 3 3 3 3 0 7 0 } RunningXor1P

Using the value of the first active element in a as a basis, this instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningXor1P uses the destination register as one of its inputs.

Vector RunningXor1P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,base,x;   base = s = 0;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))     {       base = a.v[x];       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     r.v[x] = base {circumflex over ( )} s;     if ((gPred.v[x]) && (p.v[x] ))       s {circumflex over ( )}= b.v[x];   }   return(r); }

EXAMPLES

 ~p0; a = RunningXor1P(a,b,p1);  On Entry: p0 = { 1 1 1 1 1 0 1 0 } a = { 7 6 5 4 3 2 1 0 } b = { 7 2 1 2 3 4 5 6 } p1 = { 0 1 1 0 1 1 1 0 }  On Exit: a = { 7 6 4 5 5 2 6 0 }  !p0; a = RunningXor1P(a,b,p1);  On Entry: p0 = { 1 1 1 1 1 0 1 0 } a = { 7 6 5 4 3 2 1 0 } b = { 7 2 1 2 3 4 5 6 } p1 = { 0 1 1 0 1 1 1 0 }  On Exit: a = { 7 6 4 5 5 0 6 0 } RunningXor2P

Using the value of the first active element in a as a basis, this instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningXor2P uses the destination register as one of its inputs.

Vector RunningXor2P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,base,x;   base = s = 0;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))     {       base = a.v[x];       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))       s {circumflex over ( )}= b.v[x];     r.v[x] = base {circumflex over ( )} s;   }   return(r); }

EXAMPLES

 ~p0; a = RunningXor2P(a,b,p1);  On Entry: p0 = { 1 1 1 1 1 0 1 0 } a = { 7 6 5 4 3 2 1 0 } b = { 7 2 1 2 3 4 5 6 } p1 = { 0 1 1 0 1 1 1 0 }  On Exit: a = { 7 4 5 5 6 2 3 0 }  !p0; a = RunningXor2P(a,b,p1);  On Entry: p0 = { 1 1 1 1 1 0 1 0 } a = { 7 6 5 4 3 2 1 0 } b = { 7 2 1 2 3 4 5 6 } p1 = { 0 1 1 0 1 1 1 0 }  On Exit: a = { 7 4 5 5 6 2 3 0 } RunningMul1P

Using the value of the first active element in a as a basis, this instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values prior to being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningMul1P uses the destination register as one of its inputs.

Vector RunningMul1P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,base,x;   base = s = 1;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))     {       base = a.v[x];       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     r.v[x] = base * s;     if ((gPred.v[x]) && (p.v[x] ))       s *= b.v[x];   }   return(r); }

EXAMPLES

 ~p0; a = RunningMul1P(a,b,p1);  On Entry: p0 = { 1 1  1  1  1 0  1 0 } a = { 7 6  5  4  3 2  1 0 } b = { 7 2  1  2  3 4  2 6 } p1 = { 0 1  1  0  1 1  1 0 }  On Exit: a = { 7 6 12 12 12 2 36 0 }  !p0; a = RunningMul1P(a,b,p1);  On Entry: p0 = { 1 1  1  1  1 0  1 0 } a = { 7 6  5  4  3 2  1 0 } b = { 7 2  1  2  3 4  2 6 } p1 = { 0 1  1  0  1 1  1 0 }  On Exit: a = { 7 6 12 12 12 0 36 0 } RunningMul2P

Using the value of the first active element in a as a basis, this instruction adds the cumulative amounts specified by active elements in b to this basis. Predicate p determines which elements participate in the accumulation of addends. Inactive elements prior to the first active elements are copied into the destination. This instruction stores the values after being added into the destination register. As shown below, in some embodiments, the instruction processes all elements equivalently; however, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. Note that RunningMul2P uses the destination register as one of its inputs.

Vector RunningMul2P(const Vector &a, const Vector &b, const Vector &p) {   Vector r;   int s,base,x;   base = s = 1;   for (x=0; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))     {       base = a.v[x];       break;     }     else       r.v[x] = a.v[x];   }   for (; x<VECLEN; ++x)   {     if ((gPred.v[x]) && (p.v[x] ))       s *= b.v[x];     r.v[x] = base * s;   }   return(r); }

EXAMPLES

~p0; a = RunningMul2P(a,b,p1); On Entry: p0 = { 1  1  1  1  1 0  1 0 } a = { 7  6  5  4  3 2  1 0 } b = { 7  2  1  2  3 4  2 6 } p1 = { 0  1  1  0  1 1  1 0 } On Exit: a = { 7 12 12 12 36 2 72 0 } !p0; a = RunningMul2P(a,b,p1); On Entry: p0 = { 1  1  1  1  1 0  1 0 } a = { 7  6  5  4  3 2  1 0 } b = { 7  2  1  2  3 4  2 6 } p1 = { 0  1  1  0  1 1  1 0 } On Exit: a = { 7 12 12 12 36 0 72 0 } Vector Read/Write Operations

The following section describes instructions for performing memory operations in accordance with the described embodiments. For clarity, these example instructions are described using a single data type and a single addressing mode. Thus, the described instructions provide a basic understanding of the read/write operations used in the described embodiments. In some embodiments, these instructions are extended to support different data types, addressing modes, etc. Some embodiments provide support for a virtual memory system in these instructions.

VectorRead

This instruction reads a vector of data from a vector of addresses calculated from the instruction's inputs. A vector of offsets in offset are scaled by 1, 2, 4, or 8 according to type, and added to the scalar address specified in ptr. Data is returned in the destination register, and either sign-extended or zero-padded depending on whether signed or unsigned data is loaded. If this instruction is predicated, only addresses corresponding to active elements are read. This instruction faults on any attempt to read an unmapped page. The

syntax for this instruction is:

  Vector VectorRead<type>(void *ptr, Vector offset); VectorReadFF

This instruction reads a vector of data from a vector of addresses calculated from its inputs. Only the first active element can generate a memory fault or exception. A vector of offsets in offset are scaled by 1, 2, 4, or 8, according to type, and added to the scalar address specified in ptr. Data is returned in the destination register. If this instruction is redicated, only addresses corresponding to active elements are read.

This instruction also returns a vector of page-status flags that indicate whether the address referenced by each element was valid or not. Each per-element flag is set if the element position was inactive, or if the read of the element position was valid and all other flags were set for lesser-numbered element positions. The per-element flag is clear if the read of the element position was unmapped otherwise disallowed, or if any of the lesser-numbered flag positions were clear. Software is responsible for using these flags to ensure that loop iterations corresponding to element positions that were not read are retried if the loop does not otherwise terminate in an orderly manner.

This instruction only takes a page fault if the first active address is illegal or otherwise unmapped. This allows subsequent elements to avoid paging-in data from mass storage when it is uncertain that it will actually be used.

The interface for this instruction is:

  Vector VectorRead<type>FF(void *ptr, Vector offset,   Vector pStat); VectorReadNF

This instruction reads a vector of data from a vector of addresses calculated from its inputs. This instruction will not generate any memory faults, and thus may not actually read memory if a fault should have occurred. A vector of offsets in offset are scaled by 1, 2, 4, or 8, according to type, and added to the scalar address specified in ptr. Data is returned in the destination register. If this instruction is predicated, only addresses corresponding to active elements are read.

This instruction also returns a vector of page-status flags that indicate whether the address referenced by each element was valid or not. Each per-element flag is set if the element position was inactive, or if the read of the element position was valid and all other flags were set for lesser-numbered element positions. The per-element flag is clear if the read of the element position was unmapped otherwise disallowed, or if any of the lesser-numbered flag positions were clear. Software is responsible for using these flags to ensure that loop iterations corresponding to element positions that were not read are retried if the loop does not otherwise terminate in an orderly manner.

This instruction does not fault if an address is illegal or otherwise unmapped. This provides a mechanism for software speculation to avoid paging-in data from mass storage when it is uncertain that it will actually be used. This instruction is useful when speculatively pointer-chasing, and to prefetch data that may not be accessed.

The interface for this instruction is:

  Vector VectorRead<type>NF(void *ptr, Vector offset,   Vector pStat);   Flags: ZF: Set if no elements read; cleared otherwise. VectorWriteInt

This instruction writes a vector of data in values to a vector of addresses calculated from the instruction's inputs. A vector of offsets in offset are scaled by 1, 2, 4, or 8, and added to the scalar address specified in ptr. If this instruction is predicated, only addresses corresponding to active elements are written. Write addresses should be valid, and there is no avoidance of program termination in the event of a write to an illegal or protected address. The syntax for this instruction is:

Vector VectorWriteInt(void *ptr, Vector offset, Vector values); Sequential Vector Reads and Writes

Although the embodiments described above primarily operate on memory using a gather/scatter model, alternative embodiments include a set of sequential memory read/write instructions to handle the case where memory is addressed sequentially. In these embodiments, these memory operations: (1) support predication and zeroing; (2) work on naturally aligned boundaries for any data type; and (3) support normal and first-faulting variants (to support software speculation).

VectorLEA

This instruction calculates a vector of addresses from its inputs. A vector of offsets in offset are scaled by 1, 2, 4, or 8, and added to the scalar address specified inptr. The syntax for this instruction is:

  Vector VectorLEA(void *ptr, Vector offset); VectorIndex

This instruction populates a vector by monotonically increasing a by b for each vector position. The given value of a is stored in the first element of the destination, and b is added to every position thereafter. While the example below processes all elements, predication is performed by the assignment of the result, and should be considered an integral part of this instruction. The syntax for this instruction is:

-   -   Vector VectorIndex(int a, int b)         This instruction operates as follows:

Vector VectorIndex(int a, int b) {   Vector r = 0;   int x;   for (x=0; x<VECLEN; ++x)     r.v[x] = a + b * x;   return(r); }

EXAMPLES

~p0; a = VectorIndex(1,2); On Entry: p0 = { 0 1 1 1 1  1  1 0 } a = { 9 9 9 9 9  9  9 9 } On Exit: a = { 9 3 5 7 9 11 13 9 } !p0; a = VectorIndex(1,2); On Entry: p0 = { 1 1 1 1 1  1  1 0 } a = { 9 9 9 9 9  9  9 9 } On Exit: a = { 0 3 5 7 9 11 13 0 } Executing Program Code

FIG. 20 presents a flowchart illustrating a process for executing program code in accordance with the described embodiments. As can be seen in FIG. 20, when executing program code, processor 102 receives a first input vector, a second input vector, and a control vector, and possibly a predicate vector that include N elements (step 2000). Next, using the vectors, processor 102 generates a result vector (step 2002). Generally, when generating the result vector, copies values from the input vector into selected elements in the result vector, and propagates values for other selected elements in the result vector. (The generation of the result vector is described in detail below.)

Note that we describe “possibly” receiving a predicate vector with respect to FIG. 20. Although the described embodiments can use a predicate vector when generating the result vector, these embodiments do not need to receive a predicate vector in order to generate the result vector (i.e., the predicate vector is optional). In these embodiments, if no predicate vector is received, processor 102 assumes a predicate vector for which each element contains a non-zero value.

In some embodiments, when generating the result vector, processor 102 performs some or all of a set of operations for generating the result vector in parallel (e.g., using vector execution unit 204). Hence, in these embodiments, the values to be written to the result vector can be determined in parallel for all the elements of the result vector and written to the elements of the result vector in parallel. However, in alternative embodiments, one or more of the operations for generating the result vector can be performed in series with other operations for generating the result vector. Although different embodiments can perform the operations in different ways, for clarity and brevity, we describe embodiments that perform the operations in parallel.

In the following examples, we use zero and non-zero values to describe the configuration of vectors and the performance of operations, however, in different embodiments, other values can be used. In addition, although we refer embodiments that use “left” and “right” directions to determine elements in vectors when performing operations, in alternative embodiments, the directional references could be reversed.

In the following examples, we describe “relevant” elements. In some embodiments (e.g., for embodiments of the CopyPropagate instruction and embodiments of the PropagatePostT instructions), if the predicate vector is received, a relevant element in the result vector is an element in the result vector for which the corresponding element in the predicate vector and the corresponding element in the control vector contain non-zero values. Otherwise, a relevant element in the result vector is an element in the result vector for which the corresponding element in the control vector contains a non-zero value.

In contrast, in alternative embodiments (e.g., for embodiments of the PropagatePriorF instruction), if the predicate vector is received, a relevant element in the result vector is an element in the result vector for which the corresponding element in the predicate vector or the corresponding element in the control vector contain a zero. Otherwise, in these embodiments, a relevant element in the result vector is an element in the result vector for which the corresponding element in the control vector contains a zero.

CopyPropagate

FIG. 21 presents a flowchart illustrating a process for generating a result vector in accordance with the described embodiments. More specifically, the flowchart in FIG. 21 shows operations performed for embodiments of the CopyPropagate instruction. In these embodiments, the operations shown in FIG. 21 are performed as part of step 2002 in FIG. 20. Thus, for the purposes of describing the operations shown in FIG. 21, we assume that a first input vector, a second input vector, a control vector, and possibly a predicate vector have been received, as shown in step 2000 in FIG. 20.

Recall that in the described embodiments, the predicate vector is optional and hence may not be received. If a predicate vector is not received, processor 102 assumes a predicate vector where each element contains a non-zero value and performs the operations in FIG. 21 accordingly. In other words, the predicate vector described below (e.g., with respect to step 2102 in FIG. 21, etc.) can be an assumed predicate vector.

As shown in FIG. 21, for each of the elements of the result vector in parallel (step 2100), processor 102 determines if a corresponding element of the predicate vector contains a non-zero value (step 2102). If not, processor 102 either leaves unchanged the element in the result vector (predication) or writes a zero in the element of the result vector (zeroing) (step 2104). For example, assuming that the first input vector (iv1), the second input vector (iv2), control vector (cv), and predicate vector (pred) contain the values shown, the result vector (res) could be generated as follows for zeroing:

iv1 = { 1 2 3 4 5 6 7 8 } iv2 = { 3 2 1 2 3 1 2 3 } pred = { 0 0 0 1 1 1 0 1 } cv = { 0 0 1 1 1 1 1 1 } res = { 0 0 0 X X X 0 X } Note that zeroing and predication do not depend on the value held in a corresponding element in the control vector (i.e., for predication and zeroing, it does not matter whether the control vector holds either a zero or a non-zero value).

In some embodiments, the result vector can include one or more elements that contain initial values that were computed during an earlier operation. Alternatively, the result vector can include one or more elements that contain initial values that were copied to the result vector from another vector during the generation of the result vector. The initial values in these elements are the values that are left unchanged according to predication.

Although we show the shift/propagate and the predication/zeroing operations together in FIG. 21, these operations can occur in separately in some embodiments. More specifically, in some embodiments, the operations shown in steps 2106-2114 in FIG. 21 can be performed in one (parallel) operation to generate a result vector with values for elements in the same locations as elements where predicate vector contains a non-zero value. A separate operation can then be performed to copy the result vector to a destination, with the predication/zeroing shown in steps 2102-2104 being performed during the copy operation. In the following description, for clarity and brevity, we describe embodiments where the shift/propagate and the predication take place in a single (parallel) operation.

If a corresponding element of the predicate vector contains a non-zero value (step 2102), processor 102 determines if a corresponding element in the control vector also contains a non-zero value (step 2106). If so, processor 102 sets the element in the result vector equal to a corresponding element in the second input vector (step 2108). In other words, assuming that the element in res is at location x, and using cv and pred, processor 102 determines if pred[x] && cv[x]. If so, processor 102 sets res[x]=iv2 [x]. In this way, processor 102 copies a value from an element in iv2 to res. For example, assuming iv2, cv, and pred contain the values shown, res could be generated as follows:

iv2 = { 1 2 3 4 5 6 7 8 } pred = { 0 0 0 1 1 1 1 1 } cv = { 0 0 1 1 1 1 0 1 } res = { X X X 4 5 6 X 8 } This example shows exemplary elements where both pred[x] and cv[x] contain non-zero values, for which iv2[x] has been copied to res[x]. For clarity, other elements in res are marked with an X.

If a corresponding element of the predicate vector contains a non-zero value, but the corresponding element of the control vector contains a zero, processor 102 determines if the element in the result vector is to the left of a key element position in the result vector (step 2110). In some embodiments, the key element position in the result vector is the position of an element at a leftmost position where both the corresponding element of the predicate vector and the corresponding element of the control vector contain a non-zero value. For example, assuming cv and pred contain the values shown, the key element position is located at the fourth element.

pred = { 0 1 0 1 1 1 1 1 } cv = { 0 0 1 1 1 1 0 1 } Note that the key element position does not indicate any element in a particular vector, but instead indicates a location of an element that can apply to any of the vectors. Moreover, note that in some embodiments, the key element is at a different location.

If the element in the result vector is to the left of the key element position in the result vector, processor 102 sets the element in the result vector equal to a corresponding element in the first input vector (step 2112). Note that a key element position need not be present in the result vector. In other words, there may be no element position in both the predicate vector and the control vector where both vectors contain a non-zero value. If this case occurs, the values from iv1 are simply copied to each element in res where the corresponding element in pred contains a non-zero value (which could be all of the elements in the result vector).

If the element in the result vector is at or to the right of the key element position (i.e., not to the left of the key element), processor 102 sets the element in the result vector equal to an element in the second input vector that is located at a same location as a closest relevant element in the control vector located at or to the left of the corresponding element in the result vector (step 2114). In this way, processor 102 propagates a value from left to right for locations in the result vector where the control vector contains a zero, but the predicate vector contains a non-zero value. For example, assuming iv2, cv, and pred contain the values shown, res could be generated as follows:

iv2 = { 1 2 3 4 5 6 7 8 } pred = { 0 0 0 0 1 1 1 1 } cv = { 0 0 0 0 1 0 0 1 } res = { X X X X 5 5 5 X }

The example shows that the value 5 has been written to the fifth through seventh elements of res (i.e., at vector indexes 4-6 in res). The value 5 is written to the fifth element of res because both the fifth element of cv and pred are non-zero (as described above with respect to step 2206-2208). In addition, the value of 5 is written in the sixth and seventh elements of res because both the sixth and seventh elements of cv are zero (and pred is non-zero), and the closest relevant element in cv to the left of these elements is the fifth element. In other words, the value of 5 is propagated from the element in iv2 at the same location as the last element of cv and pred that contains a non-zero value. For clarity, other elements in res are marked with an X.

PropagatePostT

FIG. 22 presents a flowchart illustrating a process for generating a result vector in accordance with the described embodiments. More specifically, the flowchart in FIG. 22 shows operations performed for embodiments of the PropagatePostT instruction. In these embodiments, the operations shown in FIG. 22 are performed as part of step 2002 in FIG. 20. Thus, for the purposes of describing the operations shown in FIG. 22, we assume that a first input vector, a second input vector, a control vector, and possibly a predicate vector have been received, as shown in step 2000 in FIG. 20.

Recall that in the described embodiments, the predicate vector is optional and hence may not be received. If a predicate vector is not received, processor 102 assumes a predicate vector where each element contains a non-zero value and performs the operations in FIG. 22 accordingly. In other words, the predicate vector described below (e.g., with respect to step 2202 in FIG. 22, etc.) can be an assumed predicate vector.

As shown in FIG. 22, for each of the elements of the result vector in parallel (step 2200), processor 102 determines if a corresponding element of the predicate vector contains a non-zero value (step 2202). If not, processor 102 either leaves unchanged the element in the result vector (predication) or writes a zero in the element of the result vector (zeroing) (step 2204). For example, assuming that the first input vector (iv1), the second input vector (iv2), control vector (cv), and predicate vector (pred) contain the values shown, the result vector (res) could be generated as follows for zeroing:

iv1 = { 1 2 3 4 5 6 7 8 } iv2 = { 3 2 1 2 3 1 2 3 } pred = { 0 0 0 1 1 1 0 1 } cv = { 0 0 1 1 1 1 1 1 } res = { 0 0 0 X X X 0 X } Note that zeroing and predication do not depend on the value held in a corresponding element in the control vector (i.e., for predication and zeroing, it does not matter whether the control vector holds either a zero or a non-zero value).

In some embodiments, the result vector can include one or more elements that contain initial values that were computed during an earlier operation. Alternatively, the result vector can include one or more elements that contain initial values that were copied to the result vector from another vector during the generation of the result vector. The initial values in these elements are the values that are left unchanged according to predication.

Although we show the shift/propagate and the predication/zeroing operations together in FIG. 22, these operations can occur in separately in some embodiments. More specifically, in some embodiments, the operations shown in steps 2206-2214 in FIG. 22 can be performed in one (parallel) operation to generate a result vector with values for elements in the same locations as elements where predicate vector contains a non-zero value. A separate operation can then be performed to copy the result vector to a destination, with the predication/zeroing shown in steps 2202-2204 being performed during the copy operation. In the following description, for clarity and brevity, we describe embodiments where the shift/propagate and the predication take place in a single (parallel) operation.

If a corresponding element of the predicate vector contains a non-zero value (step 2202), processor 102 determines if a corresponding element in the control vector also contains a non-zero value (step 2206). If so, processor 102 sets the element in the result vector equal to a corresponding element in the first input vector (step 2208). In other words, assuming that the element in res is at location x, and using cv and pred, processor 102 determines if pred[x] && cv[x]. If so, processor 102 sets res[x]=iv1[x]. In this way, processor 102 copies a value from an element in iv1 to res. For example, assuming iv1, cv, and pred contain the values shown, res could be generated as follows:

iv1 = { 1 2 3 4 5 6 7 8 } pred = { 0 0 0 1 1 1 1 1 } cv = { 0 0 1 1 1 1 0 1 } res = { X X X 4 5 6 X 8 } This example shows exemplary elements where both pred[x] and cv[x] contain non-zero values, for which iv1[x] has been copied to res[x]. For clarity, other elements in res are marked with an X.

If a corresponding element of the predicate vector contains a non-zero value, but the corresponding element of the control vector contains a zero, processor 102 determines if the element in the result vector is to the left of a key element position in the result vector (step 2210). In some embodiments, the key element position in the result vector is the position of an element at a leftmost position where the corresponding element of the control vector contains a non-zero value. For example, assuming cv and pred contain the values shown, the key element position is located at the fourth element.

pred = { 0 1 0 1 1 1 1 1 } cv = { 0 0 0 1 1 1 0 1 } Note that the key element position does not indicate any element in a particular vector, but instead indicates a location of an element that can apply to any of the vectors. Moreover, note that in some embodiments, the key element is at a different location.

If the element in the result vector is to the left of the key element position in the result vector, processor 102 sets the element in the result vector equal to a corresponding element in the first input vector (step 2212). For example, assuming iv1, cv, and pred contain the values shown, res could be generated as follows:

iv1 = { 1 2 3 4 5 6 7 8 } pred = { 1 1 1 1 1 1 1 1 } cv = { 0 0 0 1 1 1 0 1 } res = { 1 2 3 X X X X X } This example shows exemplary elements where pred[x] contains a non-zero value and cv[x] contains a zero (before the key element position), for which iv1[x] has been copied to res[x]. For clarity, other elements in res are marked with an X. Note that a key element position need not be present in the result vector. In other words, there may be no element position in both the predicate vector and the control vector where both vectors contain a non-zero value. If this case occurs, the values from iv1 are simply copied to each element in res where the corresponding element in pred contains a non-zero value (which could be all of the elements in the result vector).

If the element in the result vector is to the right of the key element position, processor 102 sets the element in the result vector equal to an element in the second input vector that is located at a same location as a closest relevant element in the control vector located the left of the corresponding element in the control vector (step 2214). In this way, processor 102 propagates a value from left to right for locations in the result vector where the control vector contains a zero, but the predicate vector contains a non-zero value. For example, assuming iv2, cv, and pred contain the values shown, res could be generated as follows:

iv2 = { 1 2 3 4 5 6 7 8 } pred = { 0 0 0 0 1 1 1 1 } cv = { 0 0 0 0 1 0 0 1 } res = { X X X X X 5 5 X } The value of 5 is written in the sixth and seventh elements of res because both the sixth and seventh elements of cv are zero (and pred is non-zero), and the closest relevant element in cv to the left of these elements is the fifth element. In other words, the value of 5 is propagated from the element in iv2 at the same location as the last element of cv and pred that contains a non-zero value. For clarity, other elements in res are marked with an X.

PropagatePriorF

FIG. 23 presents a flowchart illustrating a process for generating a result vector in accordance with the described embodiments. More specifically, the flowchart in FIG. 23 shows operations performed for embodiments of the PropagatePriorF instruction. In these embodiments, the operations shown in FIG. 23 are performed as part of step 2002 in FIG. 20. Thus, for the purposes of describing the operations shown in FIG. 23, we assume that a first input vector, a control vector, and possibly a predicate vector have been received, as shown in step 2000 in FIG. 20. (Note that although FIG. 20 describes receiving a second input vector, the second input vector is not used for the PropagatePriorF instruction and thus is not described with respect to the PropagatePriorF instruction.)

Recall that in the described embodiments, the predicate vector is optional and hence may not be received. If a predicate vector is not received, processor 102 assumes a predicate vector where each element contains a non-zero value and performs the operations in FIG. 23 accordingly. In other words, the predicate vector described below (e.g., with respect to step 2302 in FIG. 23, etc.) can be an assumed predicate vector.

As shown in FIG. 23, for each of the elements of the result vector in parallel (step 2300), processor 102 determines if a corresponding element of the predicate vector contains a non-zero value (step 2302). If not, processor 102 either leaves unchanged the element in the result vector (predication) or writes a zero in the element of the result vector (zeroing) (step 2304). For example, assuming that the first input vector (iv1), control vector (cv), and predicate vector (pred) contain the values shown, the result vector (res) could be generated as

follows for zeroing:

iv1 = { 1 2 3 4 5 6 7 8 } pred = { 0 0 0 1 1 1 0 1 } cv = { 0 0 1 1 1 1 1 1 } res = { 0 0 0 X X X 0 X } Note that zeroing and predication do not depend on the value held in a corresponding element in the control vector (i.e., for predication and zeroing, it does not matter whether the control vector holds either a zero or a non-zero value).

In some embodiments, the result vector can include one or more elements that contain initial values that were computed during an earlier operation. Alternatively, the result vector can include one or more elements that contain initial values that were copied to the result vector from another vector during the generation of the result vector. The initial values in these elements are the values that are left unchanged according to predication.

Although we show the shift/propagate and the predication/zeroing operations together in FIG. 23, these operations can occur in separately in some embodiments. More specifically, in some embodiments, the operations shown in steps 2306-2314 in FIG. 23 can be performed in one (parallel) operation to generate a result vector with values for elements in the same locations as elements where predicate vector contains a non-zero value. A separate operation can then be performed to copy the result vector to a destination, with the predication/zeroing shown in steps 2302-2304 being performed during the copy operation. In the following description, for clarity and brevity, we describe embodiments where the shift/propagate and the predication take place in a single (parallel) operation.

If a corresponding element of the predicate vector contains a non-zero value (step 2302), processor 102 determines if a corresponding element in the control vector contains a zero (step 2306). If so, processor 102 sets the element in the result vector equal to a corresponding element in the first input vector (step 2308). In other words, assuming that the element in res is at location x, and using cv and pred, processor 102 determines if pred[x] && !(cv[x]). If so, processor 102 sets res[x]=iv1[x]. In this way, processor 102 copies a value from an element in iv1 to res. For example, assuming iv1, cv, and pred contain the values shown, res could be generated as follows:

iv1 = { 1 2 3 4 5 6 7 8 } pred = { 1 0 1 1 1 1 1 1 } cv = { 0 0 1 0 0 0 0 1 } res = { 1 X X 4 5 6 7 X } This example shows exemplary elements where pred[x] contains a non-zero value and cv[x] contains a zero, for which iv1[x] has been copied to res[x]. For clarity, other elements in res are marked with an X.

If both the corresponding element of the predicate vector and the corresponding element of the control vector contain a non-zero value (step 2306), processor 102 determines if the element in the result vector is located to left of a leftmost element in the control vector or the predicate vector that contains a zero (step 231 0). If so, processor 102 sets the element in the result vector equal to a rightmost element in the first input vector (step 2312). This case occurs only when the first element in the control vector and the predicate vector both contain a non-zero value. In this case, the value from element in the last (i.e., rightmost) position of the input vector is copied to the first (i.e., leftmost) element in the result vector. The value from the rightmost position of the input vector is then propagated across any subsequent elements in the result vector until encountering the first (i.e., leftmost) element in the control vector or the predicate vector that

contains a zero. For example, assuming iv1, cv, and pred contain the values shown, res could be generated as follows:

iv1 = { 1 2 3 4 5 6 7 8 } pred = { 1 1 1 1 0 0 0 0 } cv = { 1 1 0 1 0 0 0 1 } res = { 8 8 X X X X X X } This example shows exemplary elements where pred[x] and cv[x] both contain non-zero values before a leftmost element in cv or pred that contains a zero. In these elements, iv1[N-1] has been copied to res[x]. For clarity, other elements in res are marked with an X.

If the element in the result vector is located to right of a leftmost element in the control vector or the predicate vector that contains a zero, processor 102 sets the element in the result vector equal to an element in the first input vector that is located at a same location as a closest relevant element in the control vector located the left of the corresponding element in the control vector (step 2314). In this way, processor 102 propagates a value from left to right for locations in the result vector where both the control vector and the predicate vector contain a non-zero value. For example, assuming iv1, cv, and pred contain the values shown, res could be generated as follows:

iv1 = { 1 2 3 4 5 6 7 8 } pred = { 1 1 1 1 1 1 1 1 } cv = { 0 0 0 0 0 0 1 1 } res = { X X X X X X 6 6 } In addition, the value of 6 is written in the seventh and eighth elements of res because both the seventh and eighth elements of cv are non-zero and pred is non-zero, and the closest element in cv to the left of these elements that contains a zero (i.e., the last relevant element) is the sixth element. In other words, the value of 6 is propagated from the element in iv1 at the same location as the last relevant element of cv to the right of these elements. For clarity, other elements in res are marked with an X.

The foregoing descriptions have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the described embodiments. The scope of these embodiments is defined by the appended claims. 

1. A method for propagating values to a result vector, comprising: receiving a first input vector and a control vector, and optionally receiving a predicate vector, wherein each vector includes N elements; and generating the result vector, wherein generating the result vector involves, if the predicate vector is received, for each element in the result vector at and to the right of a key element position for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector at and to the right of the key element position, if a corresponding element in the control vector contains a non-zero value, setting the element in the result vector equal to a value in a corresponding element in the first input vector; and otherwise, if the corresponding element in the control vector contains a zero, setting the element in the result vector equal to a value contained in an element at an element position in the first input vector which corresponds to a rightmost relevant element to the left of the corresponding element in the control vector.
 2. The method of claim 1, wherein if the predicate vector is received, the key element position is a leftmost element position for which both an element in the predicate vector and an element in the control vector contain non-zero values; and otherwise, the key element position is a leftmost element position for which an element in the control vector contains a non-zero value.
 3. The method of claim 2, wherein the method further comprises: receiving a second input vector, wherein the second input vector includes N elements; wherein if the predicate vector is received, for each element to the left of the key element position for which a corresponding element in the control vector contains a zero and for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector to the left of the key element position, generating the result vector involves setting the element in the result vector equal to a value in a corresponding element in the second input vector; wherein if no key element position exists, if the predicate vector is received, for each element in the result vector for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector, generating the result vector involves setting the element in the result vector equal to a value in a corresponding element in the second input vector.
 4. The method of claim 3, wherein if the predicate vector is received, generating the result vector involves, for each element in the result vector, one of: leaving the element in the result vector unmodified if a corresponding element in the predicate vector contains a zero; or setting the element in the result vector to zero if a corresponding element in the predicate vector contains a zero.
 5. The method of claim 1, wherein generating the result vector involves processing elements in the input vectors, control vector, and, if the predicate vector is received, the predicate vector in parallel to enable the elements of the result vector to be generated in parallel.
 6. The method of claim 1, wherein generating the result vector involves storing the result vector in a processor register or a computer-readable storage medium.
 7. The method of claim 1, wherein if the predicate vector is received, a relevant element is an element position where an element in the control vector contains a non-zero value and an element in the predicate vector contains a non-zero value; otherwise, a relevant element is an element position where an element in the control vector contains a non-zero value.
 8. A method for propagating values to a result vector, comprising: receiving a first input vector, a second input vector, and a control vector, and optionally receiving a predicate vector, wherein each vector includes N elements; and generating the result vector, wherein generating the result vector involves, if the predicate vector is received, for each element in the result vector to the right of a key element position for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector to the right of the key element position, if a corresponding element in the control vector contains a non-zero value, setting the element in the result vector equal to a value in a corresponding element in the first input vector; and otherwise, if the corresponding element in the control vector contains a zero, setting the element in the result vector equal to a value contained in an element at an element position in the second input vector which corresponds to a rightmost relevant element to the left of the corresponding element in the control vector.
 9. The method of claim 8, wherein the key element position is a leftmost element position for which an element in the control vector contains a non-zero value.
 10. The method of claim 9, wherein if the predicate vector is received, for each element for which the predicate vector contains a non-zero value at or to the left of the key element position, otherwise, for each element in the result vector at or to the left of the key element position, generating the result vector involves setting the element in the result vector equal to a value in a corresponding element in the first input vector; wherein if no key element position exists, if the predicate vector is received, for each element in the result vector for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector, generating the result vector involves setting the element in the result vector equal to a value in a corresponding element in the first input vector.
 11. The method of claim 10, wherein if the predicate vector is received, generating the result vector involves, for each element in the result vector, one of: leaving the element in the result vector unmodified if a corresponding element in the predicate vector contains a zero; or setting the element in the result vector to zero if a corresponding element in the predicate vector contains a zero.
 12. The method of claim 8, wherein generating the result vector involves processing elements in the input vectors, control vector, and, if the predicate vector is received, the predicate vector in parallel to enable the elements of the result vector to be generated in parallel.
 13. The method of claim 8, wherein generating the result vector involves storing the result vector in a processor register or a computer-readable storage medium.
 14. The method of claim 8, wherein if the predicate vector is received, a relevant element is an element position where an element in the control vector contains a non-zero value and an element in the predicate vector contains a non-zero value; otherwise, a relevant element is an element position where an element in the control vector contains a non-zero value.
 15. A method for propagating values to a result vector, comprising: receiving an input vector and a control vector, and optionally receiving a predicate vector, wherein each vector includes N elements; and generating the result vector, wherein generating the result vector involves, if the predicate vector is received, for each element in the result vector at or to the right of a key element position for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector at or to the right of the key element position, if a corresponding element in the control vector contains a zero, setting the element in the result vector equal to a value in a corresponding element in the input vector; and otherwise, if the corresponding element in the control vector contains a non-zero value, setting the element in the result vector equal to a value contained in an element at an element position in the input vector which corresponds to a rightmost relevant element to the left of the corresponding element in the control vector, wherein if a leftmost element in the result vector is at the key element position, for each element in the result vector to the left of a leftmost element position in the result vector where a corresponding element in the control vector or the predicate vector contains a zero, setting the element in the result vector equal to a value in a rightmost element of the input vector.
 16. The method of claim 15, wherein if the predicate vector is received, the key element position is a leftmost element position for which both an element in the predicate vector and an element in the control vector contain non-zero values; and otherwise, the key element position is a leftmost element position for which an element in the control vector contains a non-zero value.
 17. The method of claim 16, wherein if the predicate vector is received, for each element in the result vector to the left of the key element position for which a corresponding element in the control vector contains a zero and for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector to the left of the key element position, generating the result vector involves setting the element in the result vector equal to a value in a corresponding element in the input vector; wherein if no key element position exists, if the predicate vector is received, for each element in the result vector for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector, generating the result vector involves setting the element in the result vector equal to a value in a corresponding element in the input vector.
 18. The method of claim 17, wherein if the predicate vector is received, generating the result vector involves, for each element in the result vector, one of: leaving the element in the result vector unmodified if a corresponding element in the predicate vector contains a zero; or setting the element in the result vector to zero if a corresponding element in the predicate vector contains a zero.
 19. The method of claim 15, wherein generating the result vector involves processing elements in the input vector, control vector, and, if the predicate vector is received, the predicate vector in parallel to enable the elements of the result vector to be generated in parallel.
 20. The method of claim 15, wherein generating the result vector involves storing the result vector in a processor register or a computer-readable storage medium.
 21. The method of claim 15, wherein if the predicate vector is received, a relevant element is an element position where an element in the control vector contains a zero or an element in the predicate vector contains a zero; otherwise, a relevant element is an element position where an element in the control vector contains a zero.
 22. A processor for propagating values to a result vector, comprising: at least one execution unit, wherein the execution unit is configured to: receive a first input vector and a control vector, and optionally receive a predicate vector, wherein each vector includes N elements; and generate the result vector, wherein when generating the result vector, if the predicate vector is received, for each element in the result vector at and to the right of a key element position for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector at and to the right of the key element position, the execution unit is configured so that: if a corresponding element in the control vector contains a non-zero value, the execution unit sets the element in the result vector equal to a value in a corresponding element in the first input vector; and otherwise, if the corresponding element in the control vector contains a zero, the execution unit sets the element in the result vector equal to a value contained in an element at an element position in the first input vector which corresponds to a rightmost relevant element to the left of the corresponding element in the control vector.
 23. The processor of claim 22, wherein if the predicate vector is received, the key element position is a leftmost element position for which both an element in the predicate vector and an element in the control vector contain non-zero values; and otherwise, the key element position is a leftmost element position for which an element in the control vector contains a non-zero value.
 24. The processor of claim 23, wherein the execution unit is configured to: receive a second input vector, wherein the second input vector includes N elements; wherein if the predicate vector is received, for each element to the left of the key element position for which a corresponding element in the control vector contains a zero and for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector to the left of the key element position, when generating the result vector, the execution unit is configured to set the element in the result vector equal to a value in a corresponding element in the second input vector; wherein if no key element position exists, if the predicate vector is received, for each element in the result vector for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector, when generating the result vector, the execution unit is configured to set the element in the result vector equal to a value in a corresponding element in the second input vector.
 25. The processor of claim 24, wherein if the predicate vector is received, when generating the result vector, for each element in the result vector, the execution unit is configured to one of: leave the element in the result vector unmodified if a corresponding element in the predicate vector contains a zero; or set the element in the result vector to zero if a corresponding element in the predicate vector contains a zero.
 26. The processor of claim 22, wherein generating the result vector, the execution unit is configured to process elements in the input vector, control vector, and, if the predicate vector is received, the predicate vector in parallel to enable the elements of the result vector to be generated in parallel.
 27. The processor of claim 22, wherein if the predicate vector is received, a relevant element is an element position where an element in the control vector contains a non-zero value and an element in the predicate vector contains a non-zero value; otherwise, a relevant element is an element position where an element in the control vector contains a non-zero value.
 28. A computer system for propagating values to a result vector, comprising: a processor; a memory coupled to the processor, wherein the memory stores instructions and data for the processor; and at least one execution unit in the processor, wherein the execution unit is configured to: receive a first input vector, a second input vector, and a control vector, and optionally receive a predicate vector, wherein each vector includes N elements; generate the result vector, wherein when generating the result vector, if the predicate vector is received, for each element in the result vector to the right of a key element position for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector to the right of the key element position, the execution unit is configured so that: if a corresponding element in the control vector contains a non-zero value, the execution unit sets the element in the result vector equal to a value in a corresponding element in the first input vector; and otherwise, if the corresponding element in the control vector contains a zero, the execution unit sets the element in the result vector equal to a value contained in an element at an element position in the second input vector which corresponds to a rightmost relevant element to the left of the corresponding element in the control vector.
 29. The computer system of claim 28, wherein the key element position is a leftmost element position for which an element in the control vector contains a non-zero value.
 30. The computer system of claim 29, wherein if the predicate vector is received, for each element for which the predicate vector contains a non-zero value at or to the left of the key element position, otherwise, for each element in the result vector at or to the left of the key element position, when generating the result vector, the execution unit is configured to set the element in the result vector equal to a value in a corresponding element in the first input vector; wherein if no key element position exists, if the predicate vector is received, for each element in the result vector for which a corresponding element in the predicate vector contains a non-zero value, otherwise, for each element in the result vector, when generating the result vector, the execution unit is configured to set the element in the result vector equal to a value in a corresponding element in the first input vector.
 31. The computer system of claim 30, wherein if the predicate vector is received, when generating the result vector, for each element in the result vector, the execution unit is configured to one of: leave the element in the result vector unmodified if a corresponding element in the predicate vector contains a zero; or set the element in the result vector to zero if a corresponding element in the predicate vector contains a zero.
 32. The computer system of claim 28, wherein when generating the result vector, the execution unit is configured to process elements in the input vector, control vector, and, if the predicate vector is received, the predicate vector in parallel to enable the elements of the result vector to be generated in parallel.
 33. The processor of claim 28, wherein if the predicate vector is received, a relevant element is an element position where an element in the control vector contains a non-zero value and an element in the predicate vector contains a non-zero value; otherwise, a relevant element is an element position where an element in the control vector contains a non-zero value. 